Dealing with heat waves: can I use the PHPP to size cooling equipment?

Given ever more frequent heat waves and the increasing need for active cooling in Passivhaus residential buildings, the issue of correctly sizing cooling equipment is key if we are to maintain thermal comfort, at low power.

Dealing with heat waves: can I use the PHPP to size cooling equipment?

The issue of correctly sizing cooling equipment is key if we are to maintain thermal comfort, at low power

The article looks at using the PHPP for sizing cooling equipment and compares results with multi-zone calculations using dynamic simulation

Dealing with heat waves: can I use the PHPP to size cooling equipment?
Photo: Energy Vanguard

Given ever more frequent heat waves and the increasing need for active cooling in Passivhaus residential buildings, the issue of correctly sizing cooling equipment is key if we are to maintain thermal comfort, at low power. Over-sizing of cooling plant adds unnecessary cost and energy consumption, increasing stress on power grids as they try and meet peak loads, especially under heat wave conditions. Under-sizing cooling plant will lead to comfort problems, failed expectations and a performance gap that Passivhaus buildings have been consistently shown to fill. Once the work has gone into creating a working PHPP model, can we safely use the tool to size cooling kit?

The article looks at using the PHPP for sizing cooling equipment and compares results with multi-zone calculations using dynamic simulation, based on a simple worked example of a completed and certified Passivhaus residential building in climate zone 5-Warm. The research was prompted by the (painful) lessons learned some years ago, when using the PHPP to size cooling equipment for a single-family low-energy home with Passivhaus components, without adequate modification of boundary conditions. The home had active cooling but suffered from overheating problems and complaints from occupants.

Global temperature change

How does PHPP calculate cooling loads?

PHPP calculates sensible and latent cooling loads as the maximum daily average cooling power required to maintain the operative temperature set point, providing an average cooling load across the whole building, based on maximum daily average outdoor air temperature, dew point, sky temperature and solar radiation. Occupancy gains are typically based on a default setting (e.g., for TFA = 150m², occupancy ratio = 51 m²/p, occupancy = 2.9 people. 

How does a dynamic simulation tool calculate cooling loads?

Dynamic simulation tools allow for a multi-zone calculation based on hourly climate data, occupancy activity, and equipment operation, providing a time-dependent, high-resolution calculation of cooling loads. Typically, solar gains are calculated on an hourly time-step, and occupancy gains are computed dynamically, such that latent gains increase, and sensible gains decrease, as indoor operative temperature increases (people begin to sweat more as indoor temperature increases…). Is this level of accuracy really necessary, or can we use the PHPP to size cooling plant?

Which kind of tool should I use to size cooling equipment?

Finding the right answer to the question involves asking some the following questions: what building typology are we dealing with? What are the local short-term climate conditions, over 24 hours, during the hottest days? What is the occupancy density of the building, what are the internal heat gains and solar gains, and at what time in the day do they occur? Logically, a single zone, quasi-steady state calculation method such as the one found in PHPP, will be pushed to its limits for larger buildings and/or those with short-term peak gains derived from solar radiation, occupancy or equipment use, particularly if they vary greatly from one zone to the other.

Worked example: PHPP vs. dynamic simulation cooling load calculation for single-family home

Table 1 and Figure 2 shows peak cooling load results per zone, for a single-family certified Passivhaus in Mallorca, Spain, with a TFA of 170m², comparing a dynamic multi-zone calculation using DesignBuilder/EnergyPlus, with PHPP single-zone results. The PHPP climate file for the energy balancing calculations is ES0022b-Palma de Mallorca, but the climate file boundary conditions have been adjusted in the PHPP for the conditions shown in Figure 1 (derived from an hourly data set generated by Meteonorm v.7), with an outdoor air temperature of 38.1ºC and a dew point temperature of 27.2ºC (taken from the average 24-hour relative humidity of 54% @ 38.1ºC dry air temperature). The following adjustments were also made in the PHPP: the occupancy was increased to 10 people, the cooling set-point was reduced to 24ºC, and the solar factor of the glazing was increased by 5% (to eliminate the default soiling factor included in the Glazing worksheet), in agreement with the boundary conditions used in the dynamic calculation.

Climate conditions for cooling load calculation

Figure 1: Climate conditions for cooling load calculation

Results of total cooling loads

Figure 2: Results of total cooling loads

Cooling load results
Table 1. Cooling load results

The results shown in Table 1 and Figure 2 indicate a negligible 1% difference in the total average peak cooling load results at building level, between the dynamic multi-zone calculation and the PHPP results, suggesting that if the PHPP boundary conditions are modified from those used for building certification, the tool can be safely used for sizing cooling equipment for small residential buildings. This approach has been used on many projects of this type for many years with no complaints of overheating from occupants. However, if we look at peak cooling loads on a zone-to-zone basis, they vary by a + 68% (toilet) and -58% (corridor). While this has generally not been found to be a problem in practice in single-family homes, this suggests caution is required with larger buildings or for zones in smaller buildings with higher short-term peak gains (from solar radiation, occupancy or equipment use). Also, cooling distribution must be carefully planned to ensure specific zones don’t suffer from overheating and sufficient heat is removed from each zone.

Finally, the correct sizing of refrigeration equipment is important for the following reasons:

  • Oversized cooling equipment leads to higher than necessary energy consumption and therefore increased energy bills.
  • If cooling power is much higher than necessary, the setpoint temperature is reached earlier and the equipment shuts down (under orders from a thermostat, which only understands temperature, not humidity). This can lead to comfort problems due to excessively high indoor humidity.

Prefabricated passive houses, a cornerstone of Construction 4.0

Prefabrication or industrialised construction is emerging as one of the cornerstones of what is known as Construction 4.0. According to the McKinsey Global Institute, the objective of this 4th Industrial Revolution is to ditch obsolete and traditional construction methods and improve productivity by more than 50%, through- among other things- the optimization of resources based on prefabrication, zero waste and circularity.

Prefabricated passive houses, a cornerstone of Construction 4.0

Is it possible to build a prefabricated Passivhaus building? Of course it is!

Prefabrication or industrialised construction is emerging as one of the cornerstones of what is known as Construction 4.0

Prefabricated passive houses

Prefabrication or industrialised construction is emerging as one of the cornerstones of what is known as Construction 4.0. According to the McKinsey Global Institute, the objective of this 4th Industrial Revolution is to ditch obsolete and traditional construction methods and improve productivity by more than 50%, through- among other things- the optimization of resources based on prefabrication, zero waste and circularity.

Alongside this, we have the growing trend of passive houses, or homes certified to the Passivhaus standard, a voluntary certification seal that prioritises maximum comfort and indoor air quality for users, with almost zero energy consumption. It is characterised by close attention to detail in the design phase and rigorous on site control to guarantee a high construction quality, and is based on 8 principles:

  • Bioclimatic design
  • Thermal insulation
  • Air tightness
  • Reduction of thermal bridges
  • Mechanical ventilation with heat recovery
  • High performance doors and windows
  • Shading devices
  • Efficient mechanical & electrical systems

The increase in the number of buildings with Passivhaus certification during the last 10 years is notable, reaching more than 3,86 million square metres of certified floor area in 2024. In 2020, Spain was the country with the second most Passivhaus certified square metres in the world, led by China.

The marriage of prefabrication with the Passivhaus standard seems a logical step to improve construction quality, reduce execution times and increase productivity. Let’s have a look at some of these together.


Prefabrication: What is it and how is it applied to construction?

Prefabrication or industrialization is the mass production, off site, of the construction elements of a building, transferring work that was previously carried out on site to a workshop or factory. It generally includes structural elements and thermal insulation, assembled in a series of modules such as slabs, façade walls, partitions or roofs. These modules are transported to the building site and assembled, like pieces of a puzzle to form the building.

Industrialisation opens up interesting possibilities, such as the off site installation of windows, external shading systems and some services such as electricity, waste water, ventilation or heating and cooling equipment, among others.

Prefabrication: What is it and how is it applied to construction?

Advantages and drawbacks of prefabrication in passive houses

  • Rapid onsite assembly, allowing for quick weather-proofing and protection from rain and wind. This is especially important in timber construction, a material widely used in the construction of passive houses.
  • Greater precision and build quality, essential for the construction of Passivhaus buildings, above all in relation to airtightness detailing and the sealing of windows and service penetrations.
  • Less waste on site and a reduced environmental impact.
  • Optimization of materials, through standardised production and off site assembly, reducing material waste and costs..
  • Detailed design of the project has to be fully complete before manufacturing and before on-site assembly begins, and allows for fewer or no modifications once on site. It should be noted that Passivhaus projects already require detailed design to be complete before beginning construction, and allow for very little on site improvisation anyway. 
  • The time saved in assembling the prefabricated structure on site, is not always reflected in the total execution time of the building. Services, fittings and interior finishes continue to slow construction down.
  • The size of the prefabricated elements is limited, in width and height, by the size of the transport trucks and the free height on the roads that connect the factory with the construction site.

Is it possible to build a prefabricated Passivhaus building? Of course it is! Below you can find some examples

LILU´s House: bio-based Passivhaus Plus

Passivhaus design and consultancy, for this single-family house in Abrera, Barcelona, designed by architecture firm OMB Arquitectura and built by House Habitat.

Single-family home in Sitges

Single-family home in Sitges Passivhaus design & consultancy, Blower Door Tests, M & E design, Site supervision Description Passivhaus design and consultancy, M & E engineering, and…

Original article written by Oliver Style and posted at caloryfrio.com

Praxis takes part in the 15th Spanish Passivhaus Conference in Valencia

Praxis will participate in 3 sessions at the Spanish Passivhaus Conference. We would love to see you and in Valencia!

Praxis is delivering three presentations at the Spanish Passivhaus Conference in Valencia

The 15th Spanish Passivhaus Conference takes place between November 29th and December 1st.

Don’t miss the one of the key conferences in energy efficient construction, which includes 2 hours of master classes, 11 hours of technical presentations, and 5 hours of practical sessions!

Spanish Passivhaus Conference in Valencia

From November 29th to December 1st, the fifteenth Passivhaus Conference will take place at the Valencia Conference Center. Organized by the Spanish Passivhaus Building Platform (PEP), this event has become a reference meeting point in the sector and one of the main forums for innovation in Passivhaus on the Iberian peninsula.

At Praxis we are very happy to be able to participate as speakers in three presentations. Oliver Style and Bega Clavero will make their interventions on November 29th and 30th. We’d love to see you in Valencia!

Surfing the (heat) wave: can I use the PHPP to size cooling equipment?

Passivhaus Conference Valencia | Praxis Resilient Buildings

Speaker: Oliver Sytle, CEO of Praxis. Passivhaus Certifier and Consultant

Date:November 29th, from 19:00h to 20:00h


It is estimated that by 2050, there will be 6 billion air conditioning units installed in the world. Global warming is causing ever more frequent heat waves, and with rising energy costs, it is crucial to optimize passive cooling strategies and correctly size cooling equipment. In this session, we will look at how to modify the boundary conditions of the Passive House Planning Package (PHPP) to correctly size cooling equipment and achieve environmental comfort with minimal energy consumption.

Modelling of air-to-air heat pumps in the new PHPP version 10

Modeling of refrigeration systems | Praxis Resilient Buildings

Speaker: Oliver Sytle, CEO of Praxis. Passivhaus Certifier and Consultant

Date: November 30th, from 12:00h to 14:00h


The latest version of the Passive House Planning Package (PHPP) program incorporates new functionalities and the possibility of modelling cooling equipment with far greater precision than in PHPP 9.

In this technical session, Oliver will explain the data entry requirements for modelling inverter air-air cooling equipment in the PHPP10, looking at the different operating modes (“normal mode”, “silent mode”, and “dehumidification mode”) and the Energy Efficiency Ratio at maximum and minimum power.

Eco Hub #Learnlife. Passivhaus educational modules for hot climates

Eco Hub. Passivhaus educational modules for hot climates. Passivhaus Conference

Speaker: Bega Clavero, Chief Project Officer at Praxis. Passivhaus Tradesperson

Date: November 30th, from 15:45 to 17:20h


In a context where climatic conditions and air quality in Spanish educational centers are inadequate in 84% of the time, the creation of comfortable, adaptable, and healthy learning environments with good air quality and very high energy efficiency, suitable for warm climates, is a priority.

In this session, Bega Clavero will present Eco Hub, an educational module with Passivhaus Classic certification designed for warm climates with ex-situ construction techniques, designed and developed by Learnlife. The building is a learning centre, based on a scalable construction system that is adaptable to the needs of each institution, prefabricated and modular, removable and transportable to any other location, and built with low-emission and low embodied energy materials.

 

Radon gas: invisible and lethal. What is it and how to prevent it?

Radon gas is a naturally occurring radioactive gas that can enter buildings. It is currently the second most predominant cause of lung cancer after tobacco.

Radon gas: invisible and lethal. What is it and how to prevent it?

Radon gas is a naturally occurring radioactive gas that can enter buildings. It is currently the second most predominant cause of lung cancer after tobacco. It’s colorless, tasteless and has no smell, and is produced from the natural radioactive decay of uranium, present in many types of soils and rocks.

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Figure 1: Gas radon [Source Dreamstime]

How is radon gas measured in a building?

Becquerels (Bq) is the measurement of radioactivity. A becquerel corresponds to the transformation or decay of 1 atomic nucleus per second. In the air, radon concentration is measured by the number of transformations per second in one cubic meter of air (Bq/m3).

The national annual average reference level, set out by WHO in its “WHO Handbook on Indoor Radon: A Public Health Perspective”, is 100 Bq/m3. If this level cannot be reached due to country-specific conditions, the level should not exceed 300 Bq/m3.

Radon measuring devices are divided between passive and active detectors, with an uncertainty range of between 8% and 25%, depending on the type of device. The most common devices are usually passive, logically cheaper than active ones, and incorporate trace sensors for alpha particles, or ion electret chambers, to measure radon concentration.

As the concentration of the gas in indoor air can increase significantly in the short term (hours), is recommended to take long-term measurements (for example, 3 months). If the building has a ventilation or HVAC system, it is convenient to take measurements with the system on and off, in both cases for a long period time.

There are low-cost types of equipment such as the RadonEye RD200, or Airthings Wave, shown in Figure 2 and Figure 3.

Figure 2: RadonEye RD200, low-cost radon gas meter [Source: Radonova]
Figure 3: Airthings Wave, low-cost radon gas meter [Source: Airthings]

Radon gas and the Spanish building regulations

In 2019, and for the first time, Spanish building regulations established the scope and requirement of radon gas with a reference level for the average annual radon concentration inside habitable premises of 300 Bq/m3 (triple of what is recommended by the WHO).

Applicable to all new buildings, extensions, changes of use, or refurbishment of existing buildings, the regulations require the following measures, according to the risk area:

Level 1:

  • Radon barrier between living spaces and the ground
  • Ventilated air gap between the living spaces and the ground

Level 2:

  • Radon barrier between living spaces and the ground
  • Additional protection system:
    • Ventilated air gap between the living spaces and the ground
    • Ground depressurization system that allows the gas to dissipate from the ground.

The radon gas map of Spain according to the HS6 level 1 and 2 classification is shown in Figure 4.

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Figure 4: Map of radon gas in Spain [Source: Institute for Geoenvironmental Health]

How does radon gas enter a building and how to avoid it?

Radon enters a building through the fissures and openings in the envelope, especially in parts of the building in contact with the ground (slabs, basement walls, etc.), where the concentration of the gas is generally higher on the floors above (ground and first floor, etc). This is accentuated in the building during the heating period, where warm air rises, and the stack effect creates air infiltration of air on the lower floors (and exfiltration on the upper floors).

Radon gas entry is reduced and/or eliminated by a gas-resistant membranes, with a diffusion coefficient against radon less than 10-11 m2/s. An example is shown in Figure 5. The barrier must be continuous, taped and sealed at all joints and service penetrations. It is advisable to conduct a Blower Door test during the construction phase to detect leaks and repair them.

In Level 1 areas, as an alternative, it is possible to build a ventilated crawl space between the living areas and the ground, although it is a less safe solution than a radon barrier.

In Level 2 areas, the radon barrier is essential, along with a ventilated crawl space or a ground depressurization system.

The ground depressurization system consists of installing a network of perforated intake ducts, with mechanical extractors that conduct the air to the outside, above the building. This system has the same drawbacks as the ventilated crawl space and depends on a mechanical system.

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Figure 5: Radon gas resistant membrane, Ampack Sisalex 871

Although few epidemiological studies have been conducted on the possible link between radon gas in drinking water and the incidence of stomach cancer, a study by Kyle P Messier and Marc L Serre of the University of North Carolina, USA indicates that increases the risk of stomach cancer. Therefore, water becomes a double entry route, by ingestion of contaminated water or by breathing radon gas evaporated from drinking water. Under normal circumstances, the amount of radon inhaled when breathing is greater than that ingested when drinking.

Radon in drinking water can be reduced and/or eliminated by employing granular activated carbon filters, but the filter itself can accumulate radioactivity and should be located outside the thermal envelope (in a garage, for example), taking care of its treatment as toxic waste at the end of its useful life.

Study of the incidence of radon gas in 122 homes in Ireland

Barry Mc Carron, Xianhai Meng, and Shane Colclough conducted a radon gas measurement study on 122 homes in Ireland, 97 Passivhaus-certified homes, and 25 conventional homes (reference). The results can be seen in Figure 6. The average level of radon gas inside the Passivhaus dwellings was below 40 Bq/m3, both on the ground and first floors. However, in conventional homes, the average level was 104 Bq/m3 on the lower floor, and 69 Bq/m3 on the first floor.

The differences clearly show the effectiveness of airtight construction to prevent the entry of radon gas: one of the requirements of the Passivhaus certification is to have a level of air infiltrations n50 ≤ 0.60, verified by an air-tightness test.

But not only this, Passivhaus homes have a mechanical ventilation system with heat recovery, which constantly renews the air, eliminating stale and polluted air, and introducing fresh and filtered air. This can be seen in the graph in Figure 7, where Professor Walter Reinhold Uhlig of the HTW University of Dresden, measured radon gas in a Passivhaus dwelling with a mechanical ventilation system on and off. With the ventilation turned off, in certain rooms the radon level increased to 350 Bq/m3, having remained below 100 Bq/n3 with the ventilation working.

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Figure 6: Radon gas measurement results in 122 homes in Ireland [Source: McCarron et al 2020]
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Figure 7: Measurement of radon gas concentration in a Passivhaus dwelling, with and without controlled ventilation [Source: Prof. Walter Reinhold Uhlig]

Considering how lethal it is, radon gas has- surprisingly- gone unnoticed among many professionals in the sector, public administrations, and health professionals. Thanks to increased awareness and the update of the Spanish building regulations, it’s an issue we clearly can’t ignore: we need to prevent radon from entering our buildings, and ensure correct ventilation! The empirical results shown above indicate that an air or radon gas barrier, together with a mechanical ventilation system, is a highly effective combination to reduce the entry of radon gas into a building and thus protect the health of users.

Multi-family building in El Carmel 

Description Energy consultancy for a multi-family building in El Carmel, a neighbourhood in the north of Barcelona, designed by Vora Arquitectura studio. This 544 m2 building, has a ground floor and 6 upper floors, on a sloped site in Mount Carmel. Each floor has one or two apartments, with a total of 7 units.  Praxis …

Multi-family building in El Carmel

Energy consultancy

Praxis cabecera proyectos

Description

Energy consultancy for a multi-family building in El Carmel, a neighbourhood in the north of Barcelona, designed by Vora Arquitectura studio.

This 544 m2 building, has a ground floor and 6 upper floors, on a sloped site in Mount Carmel. Each floor has one or two apartments, with a total of 7 units. 

Praxis has delivered the thermodynamic simulation in Design Builder (EnergyPlus), focusing on the analysis and optimization of passive systems: analysis of solar gains, optimization of thermal insulation and bioclimatic buffer zone balcony spaces. The modelling helped us deliver the thermal and airtight envelope specification, window and shading systems specification, including a study of the impact of heat recovery in the ventilation system on energy demands.

Praxis also undertook an embodied energy study, comparing the carbon footprint and costs of different construction assemblies for external walls, with the aim of choosing an economically viable, energy efficient and sustainable solution. 

Year: 2021

Location: Barcelona

Services: Thermodynamic simulation   

Freshen up: active cooling with radiant ceilings in a Passivhaus retrofit 

The article presents an active cooling system using the supply air of the ventilation system with radiant ceiling panels, installed in a multi-residential building in the historic center of Girona, certified Passivhaus EnerPHit – Demand method.

Freshen up: active cooling with radiant ceilings in a Passivhaus retrofit

The article presents an active cooling system using the supply air of the ventilation system with radiant ceiling panels, installed in a multi-residential building in the historic center of Girona, certified Passivhaus EnerPHit – Demand method. For each apartment, the system consists of an air-source heat pump, a mechanical ventilation unit with heat and moisture recovery (MVHR), a coiling coil on the supply air stream, and radiant ceiling panels. Control is carried out with a home automation system, with temperature and humidity sensors in each room. The solution offers both heating and cooling, working quietly and at low temperature, providing high thermal comfort and efficient performance when used with a heat pump. Reliable performance depends on correct system sizing, proper commissioning of the control system and of ventilation flow rates, and user maintenance and replacement of filters in the MVHR units. Systems such as this are not a good solution in homes where windows are open a lot on the summer and are better suited to warm and dry climates with lower levels of humidity. 

The building is a multi-residential 6-storey building in the historic center of Girona, certified by Passivhaus EnerPHit – Demand method [Figure 1].  This private initiative – which was the first of its kind in Catalonia – put 4 new apartments of 129 m2 and a duplex of 162 m2 on the market.  

Due to local heritage building regulations, insulation had to be installed inside, with some loss of thermal inertia. Active cooling using a cooling coil on the the ventilation supply air is a relatively simple concept which can be cost effective to install. However, thermal power can be limited when temperatures peak. The system presented here combines supply air cooling with radiant ceiling panels, to provide sufficient power to cover peak cooling loads.  

Figure 1: completed building

The project data and team are shown below: 

  • Certification class: Passivhaus-EnerPHit – Demand Method 
  • Useful / gross floor area: 678 m2 / 1.038 m2 
  • Developer: MBD Real Estate Group  
  • Builder: Busquets Sitja  
  • Architects: López-Pedrero-Roda Architects  
  • M & E Engineering: PGI Engineering 
  • Control/home automation: Progetic 
  • PHPP, Passivhaus design: Oliver Style, Bega Clavero 
  • Passivhaus Certification: Energiehaus Arquitectos  

Description and operation of the system 

Given space and floor-to-ceiling height limitations, 2 cooling systems were initially considered: 

  1. Ventilation supply air cooling only 
  1. Ventilation supply air cooling + radiant ceiling panels 

The second option was chosen, given that operative temperatures in the summer could not be maintained at ≤ 25ºC using ventilation supply air cooling only. With 19 m2 of radiant ceiling panels (covering around 15% of the ceiling surface area), peak cooling loads could be met, calculated for an outdoor air temperature of 34.1 ºC, with an absolute humidity = 10,5 g/kg [1].  

For each apartment, the system included the following equipment: 

  • Heat pump: Daikin EWYQ005ADVP air-water monobloc heat pump (5.20 kW cooling / 5.65 kW heating) [Figure 2] 
  • Heat & moisture recovery ventilation unit: Zehnder ComfoAir550 enthalpic [Figure 3] 
  • Cooling coil: Zehnder ComfoPost CW10 [Figure 4] 
  • Radiant ceiling panels: Zehnder NIC 150 & NIC 300 [Figure 5] 
  • Control system: 
  • 1 temperature & humidity sensor per room 
  • 1 Loxone mini server [Figure 7] 
  • Various elements providing on/off control of the heat pump, 3-stepped control of the ventilation flow rate, and on/off control of each radiant ceiling circuit and control of water supply temperature to the radiant ceiling panels with a 3-way valve
Figure 2: Monobloc air-to-water heat pump
Figure 3: Energy recovery unit
Figure 4: Coiling coil, silencer, and supply air ducts (prior to insulation of ducts)
Figure 5: Radiant ceiling panels, prior to fixing on non-radiant panels 
Figure 6: Infrared image of radiant ceiling panels 
Figure 7: Control system switchboard 

In heating mode, the heat pump generates hot water, circulating it through the radiant ceiling panels at a supply/return temperature of 45 ºC / 40 ºC. At the same time, the coil on the ventilation supply air stream heats the air to around 40ºC. The fan speed is controlled to avoid excessively high flow rates, and which can lead to low relative humidity of indoor air. 

In cooling mode, the heat pump generates cold water, circulating it through the radiant ceiling panels at a supply/return temperature of 7 ºC / 12 ºC. At the same time, the coil on the ventilation supply air stream cools air to around 15 ºC. The coil also provides some dehumidification of the supply air, lowering the ambient indoor air dew point temperature and preventing condensation on the ceiling panels. In cooling mode, controlling the temperature of rooms individually is not possible given that the cooling coil only works for the entire apartment. 

The heat and moisture recovery ventilation unit also helps to increase the relative humidity of the indoor air in winter and decrease it in summer, improving thermal comfort and reducing the dehumidification load that the cooling coil needs to overcome. 

With the ventilation flow rate of 0.4 ach (135 m3/h), radiant ceiling panels typically cover – for both heating and cooling – approximately 65% of thermal loads. The ventilation system with the heating/cooling coil covers the remaining 35%. 

Radiant cooling systems must have a robust control system, to avoid problems of surface condensation. Temperature and humidity sensors were therefore installed in each of the 5 rooms where the radiant panels were located (dining room, kitchen and 3 bedrooms). The water temperature of the panels is adjusted with a 3-way mixing valve, based on the temperature and humidity data from the sensors in each room, ensuring the panel surface temperature remains above the dewpoint, avoiding condensation.  

The control system also modulates the ventilation unit’s fan power, lowering or raising the flow rate depending on the temperature setpoint and dehumidification needs. A schedule prevents the fan from operating as full flow at night, to avoid noise problems. If maximum power is required at night this can be a problem. The control allows you to set different setpoint temperatures according to specific schedules or occupancy rates, for each day of the week. 

In its default setting, the ventilation system works automatically with pre-established schedules (with the possibility of manual adjustment by occupants). Figure 8 summarizes its operation: 

Figure 8: Ventilation speeds and schedules  

Conclusions 

Cooling with radiant ceilings can offer an efficient solution that adds power to ventilation supply air cooling systems in Passive Houses in the summer. As the system is predominantly radiant and running at low temperature, it provides good comfort and can be more efficient than convective systems. Ceiling panels can be sized to meet heating and cooling loads, which in residential buildings retrofitted to Passivhaus standard means a coverage of between 15% to 30% of the ceiling surface area. This replaces ducted fan-coil or split systems, which take up more space in suspended ceilings, often a limitation in retrofit.  

The control system presented here offers a flexible solution at a reasonable cost, with a relatively user-friendly interface. The possibility of visualizing and monitoring data remotely and in real time, facilitates the optimization of the system and helps in terms of preventive maintenance. 

Systems such as this are not a good solution in homes where windows are open a lot on the summer and are more suitable for use in hot dry areas, since, in areas of high humidity, the power of the system will be limited depending on the humidity level of the indoor air and the proximity to the dew point. Robust operation depends correct system sizing, proper commissioning of the control system and of ventilation flow rates, and user maintenance and replacement of filters in the MVHR units. 

Passivhaus in the Mediterranean? Strategies for keeping cool in a Passivhaus on the beach 

A significant rise in temperatures is expected in the Mediterranean area in the coming years. Therefore, identifying and implementing effective strategies to reduce indoor temperatures in buildings and reduce the need for air conditioning is increasingly important.

Passivhaus in the Mediterranean? Strategies for keeping cool in a Passivhaus on the beach

According to the climate modelling presented in the study “Study on Climate Change and Energy in the Mediterranean” carried out by the European Investment Bank, countries in the Mediterranean basin will experience an increase of between 3ºC – 6ºC in average temperatures between the period 2070-2099, based on the 1961-1990 period.

Figure 1: Climate modelling of the Mediterranean basin; average annual variation of air temperatures in summer (°C), 2070-2099 vs 1961-1990

The need to tackle overheating is addressed directly in the European Directive 2010/31/EU for nearly zero energy buildings (nZEB), which states the following: “Priority should be given to strategies that improve the thermal performance of buildings in the summer. To this end, measures should be promoted to prevent overheating, such as shading and sufficient thermal inertia in the construction of buildings, as well as to improve and apply passive cooling techniques (…)” [2]. This article presents the strategies used to improve the thermal performance in summer of a passive house in a Mediterranean climate. 

Caste study: “Esencia Mediterránea”…passive house on the beach 

The home, “Esencia Mediterránea,” has a useful area of 173m2, over two floors, located about 50 meters from the beach, 3 m above sea level (Figure 2, Figure 3, Figure 4) It has an architectural design very much in line with the Mediterranean vernacular tradition, was designed by Guillermo and Iciar Sen, built by House Habitat, and is Passivhaus certified. 

Figure 2: Satellite image, province Barcelona
Figure 3: Satellite image, Castelldefels 
Figure 4: Ground floor 
Figure 5: First floor
Figure 6: Photo of the home [Source: House Habitat] 

The project team:  

  • Architects: Guillermo Sen, Iciar Sen 
  • Technical Architect: Javier García Garrido – Garcia & Sala Arquitectes  
  • Builder: Pere Linares – House Habitat  
  • PHPP & building physics: Oliver Style, Bega Clavero  
  • HVAC design: Vicenç Fulcarà – Progetic 
  • Passivhaus and Blower Door Certification: Micheel Wassouf, Martín Amado – Energiehaus 

Passive cooling strategies 

Many of the strategies used to improve the summer performance of the home are rooted in traditional Mediterranean vernacular architecture and combined with modern solutions. For the thermal analysis presented here, a PHPP model of the house was prepared to meet the minimum requirements of the Spanish Building Code (CTE). Subsequently, the impact of each strategy on cooling demand is presented, until the limiting cooling demand value required by the Passivhaus standard is achieved. 

Shading analysis 

In order to be able to more accurately check the impact of design strategies for the summer, a shadow study was carried out with the DesignBuilder – EnergyPlus thermo-dynamic tool(Figure 7, Figure 8, Figure 9). The results were used to calculated shading reduction factors for each window, that were later introduced in the PHPP shading tab. 

Figure 7: Tree canopy
Figure 8: Dynamic model for shading analysis 
Figure 9: Dynamic model for shading analysis 

Thermal inertia and natural night ventilation 

Combining thermal mass with natural cross ventilation is a key Mediterranean passive cooling strategy. Cooling power is logically limited when minimum night-time temperatures are not sufficiently low (< 18 ºC), so the strategy tends to work best in climates that are inland and at a higher altitude than coastal areas. While lightweight Passive Houses in warm climates have shown good summer performance [3, 4], some thermal inertia, in combination with night ventilation, clearly helps to modulate indoor temperatures and dissipate heat, improving comfort conditions and reducing cooling energy consumption. The house in question was built with a lightweight timber system – inherently low inertia. To incorporate some mass and enhance the effect of natural night ventilation, a 5 cm of mortar layer with ceramic floor tiles were installed on the floors of both floors, providing a specific capacity of 85 Wh/K·m2 inertia (compared to a very light building of 60 Wh/K·m2). With tilt-and-turn windows partially opened at night, a minimum night ventilation air change rate of 0,8/h was calculated with the PHPP tool, provided by simple, cross and stack effect ventilation. 

Reflective surfaces: walls and roofs 

White painted walls and roofs are another feature of traditional Mediterranean architecture. The house has a white silicate mortar render, with a white roof, both with a solar absorption factor of α = 40 % (black α = 95 %). This helps to reflect more solar radiation and reduces transmission heat gains to the interior of the house. 

Shading devices and solar control 

Solar gains are reduced with balconies set back from the façade, exterior shading devices, and solar control glazing with a solar factor of 36%.

Thermal insulation 

Thermal insulation reduces transmission heat gains, especially through roofs. It is important to find a balance between the insulation thicknesses needed for winter and summer, since an excessive thickness of insulation can in some cases prevent heat dissipation at night in the summer. On the ground floor, 15 cm of wood fibre insulation was used, U = 0.264 W/m2·K. On external walls, 20 cm of wood fibre insulation was installed between the timber structure with 6 cm of external high-density wood fibre insulation, U = 0,158 W/m2·K. The roof has 26 cm of wood fibre insulation, for a U = 0,152 W/m2·K 

Air infiltration 

Reducing air ex/infiltration is a strategy that comes from cold and temperate climates, where the priority is to reduce winter heat losses, when there can often be an indoor-outdoor ΔT of 30 ºC. Outdoor air temperatures would have to be 55 ºC to have the same ΔT in summer. However, reducing air infiltrations in coastal Mediterranean climates with high humidity can help reduce latent cooling loads when active cooling is on and windows are shut. In the case study home presented here, reducing air infiltration from n50 = 5 ach (a typical value for newly built homes) to n50 = 0.4 ach, the latent cooling load is reduced by 39% and the latent cooling demand by 7%. 

Mechanical ventilation with heat and moisture recovery (enthalpy) + automatic bypass in summer 

Mechanical ventilation with heat recovery (MVHR) is another solution that originated in central and northern Europe. Does it work in a Mediterranean summer? When outdoor temperatures rise above the indoor comfort temperature (> 25 ºC), users in air-conditioned Mediterranean homes typically close windows and turn on the cooling system, with negative consequences for indoor air quality. A mechanical ventilation system with heat recovery and automatic summer bypass, ensures constant air change and high air quality. When Tout > Tint the heat recovery unit reduces the temperature of the inlet air, shown in Figure 10, where heat recovery reduces the temperature of incoming air from 35.5 ºC to 29.5 ºC:

Figure 10: Mechanical ventilation with heat recovery in the summer  

When Tout < Tint the automatic bypass opens, providing free cooling and bypassing heat recovery. Additionally, an enthalpy unit reduces the amount of water vapor that enters the house in summer when the absolute humidity of the outdoor air is greater than the extract air (which is often the case in warm humid climates in homes with air conditioning / dehumidification). When the air conditioning is off, users can of course open windows at any point.  

Discussion and conclusions 

Figure 11 shows the PHPP simulation results for each of the strategies described above. The reduction in cooling demands from insulation on the roof is less than on the walls – a result that seems surprising. This is due to shading from the tree canopy, which means the reduction is less than in the walls. The results show that the combination of all strategies is greater than the sum of individual strategies. Cooling demand is reduced from 33 kWh/m2·a with the CTE code-compliant building, to 18 kWh/m2·a, meeting the requirements for the Passivhaus certification in a Barcelona climate.  

Figure 11: PHPP simulation results, cooling demands 
 

Combining traditional Mediterranean passive cooling strategies with solutions included in the Passivhaus standard, the summer performance of buildings can be improved with a reduced need for air conditioning.  “Stress testing” your design with a tool such as PHPP in the early stages of the project is essential, and post-construction monitoring and evaluation is highly recommended to learn from mistakes and improve.

References 

[1] Somot, S. (2005), “Modélisation climatique du bassin Méditerranéen: Variabilité et scénarios de changement climatique.” Thése de Doctorat, Université Toulouse III-Paul Sabatier. UFR Sciences de la Vie et de la Terre. pp 347. Toulouse, Francia, 2005. 

[2] Parlamento Europeo (2010), “Directiva 2010/31/UE del Parlamento Europeo y del Consejo, de 19 de mayo de 2010, relativa a la eficiencia energética de los edificios (refundición)”. Parlamento y Consejo Europeo, Bruselas, 2010. 

[3] Wassouf, M. (2015), “Comfort and Passive House in the Mediterranean summer – monitorization of 2 detached homes in Spain Barcelona”, 19th IPHC, Leipizig, Alemania.  

[4] Oliver Style (2016), “Measured performance of a lightweight straw bale passive house in a Mediterranean heat wave”. 20th International Passivhaus Conference, Darmstadt, Alemania. 

Lessons learned during 10 years of Passivhaus projects

Lessons learned during the design and construction of Passivhaus buildings over the past 10 years in Spain, identifying the importance of the heat loss form factor, along with successes and pitfalls related to thermal insulation, windows, airtightness, ventilation and active systems.

Lessons learned during 10 years of Passivhaus projects

The Heat Loss Form Factor: Keep it boxy but beautiful!

The compacity of a building has a large influence on energy performance, measured by the form factor, which is the ratio between the thermal envelope and Treated Floor Area (Athermal envelope [m2] ÷ TFA [m2]). The greater the form factor, the greater the exposed heat loss area of the envelope per m2 of TFA, requiring higher levels of thermal protection to achieve the same level of energy efficiency. To illustrate the fact, PHPP modelling results from a range of Passivhaus Classic buildings have been analysed, for varying typologies (single-family, multi-residential, offices and nursing homes) across different Spanish climates. The Form Factor has been compared with two parameters: insulation thickness, using an equivalent thermal conductivity of 0.040 W/m·K (Figure 1) and average Uwindow thermal transmittance (Figure 2).

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Figure 1: Form factor vs. insulation thicknesses
Figure 2: Form factor vs. Uw installed

As expected, the results show a clear correlation: the higher the form factor, the greater the insulation thickness required, and the lower the Uwindow. The results also indicate that other factors also play a part, such as orientation, solar gain, thermal bridges and- to a lesser extent- thermal inertia.

Blower door test: the moment of truth

In timber construction, OSB boards are often used as the airtight layer and vapour retarder. Research by the Passivhaus Institut [Peper 2014] shows a wide range of air permeability between different manufacturers of OSB boards, with 22mm OSB 4 generally showing best airtightness. Table 1 shows Blower Door results in which different grades and thicknesses of OSB were used:

Table 1: Results of the Blower Door test of three lightweight timber frame houses

The sample is very small, but the results suggest that 18 mm OSB 3 is sufficient to achieve an airtightness of n50 ≤ 0.6/h, as long as all joints and connections are well sealed. Taping a plastic sheet to a 1m2 area of the OSB board (not across joints), prior to the depressurization test, can provide a simple and visual means of assessing the air permeability of an OSB board.

Airtightness in sliding windows

Sliding windows are a standard feature in Mediterranean Spanish homes, which can present challenges in terms of airtightness. Lift and slide windows can now achieve Class 4 air permeability, making them suitable for Passivhaus buildings. However, Blower Door test results with three sliding panes have shown to be problematic (Table 2), with the best results achieved at least one fixed pane. If there are several sliding panes, best results were found with the fixed pane in the centre position.

Table 2: Results of the Blower Door test of 3 buildings with sliding window frames

Table 2: Results of the Blower Door test of 3 buildings with sliding window frames.

Heating, cooling, and ventilation, better not together

The experience of using the ventilation system for heating and cooling, whereby a water-fed heating/cooling coil heats or cools ventilation supply air, has been shown to be problematic, above all during summer heat waves, in humid Mediterranean climates in urban settings. Conditioning outdoor air, rather than recirculating indoor air, means that the increase in heating and cooling power is far from linear as flow rates are increased. Also, flow rates are generally small, further limiting heating/cooling power. Despite thermal insulation sleeves on supply air ventilation ducts, long duct runs have been shown to incur large heat losses in heating mode, and large heat gains in cooling mode, meaning that valve supply temperatures at the end of the duct run are often much lower than those used in the calculations during the design phase.

References

[Burrell 2015] Burrell, E.: What is the Heat Loss Form Factor? Searched on September 9th 2019, accessible at https://elrondburrell.com/blog/passivhaus-heatloss-formfactor/

[Peper 2014] Peper, S.; Bangert, A.; Bastian Z.: Integrating wood beams into the airtight layer. Passive House Institut. 2014

Keep cool and carry on: Passivhaus cooling experiences in the warm climates

With rising global temperatures and increasingly frequent summer heat waves, keeping cool in Passive House buildings has become a hot topic.

Keep cool and carry on: Passivhaus cooling experiences in the warm climates

With rising global temperatures and increasingly frequent summer heat waves, keeping cool in Passive House buildings has become a hot topic.

Bad jokes aside, overheating can be deadly: in France the peak mortality rate during the 2003 heat wave was higher than during the first wave of COVID in 2020, shown in Figure 1 [Parienté et al 2021].

Figure 1: Mortality rate in France during 2003 heat wave vs. first wave of COVID 2020
[Source: Parienté et al 2021]

Active cooling in all climates warmer than warm-temperate looks like it will become standard. The question is: for cool-temperature climates, is passive cooling sufficient, or is active cooling unavoidable? What are the pros and cons of the different systems? Will my client ring me up during the next heat wave and give me an ear full?

The article provides technical analysis and lessons learnt from 10 years of experience applying passive and active cooling strategies in residential Passive House buildings in Catalonia, Spain. 6 different kinds of active cooling systems that have been designed and installed in single-family Passivhaus homes are compared, assessing the simplicity or complexity of design, installation, and commissioning; upfront costs; user-friendliness, robustness, and comfort; environmental impact of refrigerants for active cooling systems; and the bottom line: measured performance and monitoring data.

Passive cooling

Careful design, moderately sized and well shaded openings, close attention to local climate, and active users have been found to be some of the key drivers of successful passive cooling. Reduction of internal heat gains is key, with efficient appliances and compact Domestic Hot Water (DHW) systems that avoid the need for recirculation circuits. If recirculation circuits are unavoidable, they need high levels of insulation and flow rate control, with reduced DHW water supply temperatures- so long as this is compatible with Legionella prevention. Ultrafiltration and chemical shock disinfection are promising alternatives to the conventional solution of high DHW supply temperatures and thermal shock prevention.

External shading devices are essential, ideally with motorised external blinds, either user controlled or automated. Even north facing windows in Passivhaus buildings need shading: the very long time constant of Passivhaus buildings mean diffuse solar radiation can cause overheating. If only fixed shading can be used, then appropriate solutions for each orientation are key, with particular attention to east and west facing glazing, which receive more solar radiation in the summer than south-facing glazing (shown in Figure 2). Deep horizontal overhangs on southern glazing work best (or northern glazing in the southern hemisphere), with slanted vertical fins for east and west-facing glazing.

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Figure 2: Solar radiation by orientation, Barcelona PHPP climate file

Natural night ventilation combined with thermal inertia works well when night temperatures are sufficiently low. Cool external colours, high levels of insulation on roofs, ground coupling, and ceiling fans, are also effective strategies. Figure 3 shows an example of measured data for a single-family home employing many of those strategies (but with little thermal inertia).

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Figure 3: Collsuspina, passive cooling

Passive cooling is in general simple, low-cost, easy to install, maintain and commission, and can deliver good performance. However, passive cooling strategies are highly climate dependent and rely on careful user behaviour. Where average air temperatures and levels of solar radiation are high (hot ground), minimum night temperatures do not drop below ~ 20 ºC (limited cooling power from natural night ventilation), and night sky temperatures and outdoor air humidity are high, passive cooling won’t work. In this case, active cooling is unavoidable to maintain comfort. Figure 4 and Figure 5 show an example of climate conditions in which passive cooling strategies won’t work, during the 2015 heat wave in Barcelona, Spain.

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Figure 4: Outdoor air temperature, Barcelona 3 – 10 July 2015
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Figure 5: Outdoor absolute humidity, Barcelona 3 – 10 July

Active cooling

6 different cooling systems that have been designed and installed in residential Passive Houses are compared, assessing 6 criteria through a simple 1-to-5 point scoring system, shown in Table 1. Monitored data is provided for systems System 1, 2, 5 and 6.

Table 1: Quantitative comparison of 6 different cooling systems

Radiant cooling systems offer a high level of comfort and efficiency, but are more complex to design, install and commission, with higher capital cost. Humidity control and cooling power has been found to be problematic in warm and humid climates, where users go in and out of the house (garden/balcony etc.). Monitored data for an underfloor cooling system is shown in Figure 6. Figure 7 shows monitored data for a radiant ceiling system.

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Figure 6: System 1, Terrassa, underfloor cooling + dehumidification of ventilation supply air
Figure 7: System 2, La Garriga, radiant ceiling + dehumidification of ventilation supply air

Low-temperature radiators (set in the floor, or wall-mounted) offer a reasonable balance between simplicity, cost, efficiency, and comfort, albeit with less cooling power than fan-coils and splits, requiring a greater number of individual units to cover the same given area than a ducted fan-coil/split system (where 1 indoor unit can cool several rooms). Figure 8 shows monitored data for this kind of system.

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Figure 8: System 3, Moià, low-temperature radiators

Supply air cooling has been found to be problematic, due to limited cooling power (a consequence of conditioning outdoor air rather than recirculating indoor air, low flow rates, and heat gain along long duct runs). Power can be increased using partial recirculation but monitored data in Figure 9 shows that temperature and relative humidity often move outside the extended comfort range. The advantages of this kind of system are simplicity and low capital cost, but the limited cooling power means passive cooling measures must be robust: once overheating has set in, the system will struggle to eliminate heat.

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Figure 9: System 4, Girona, supply air cooling + recirculation

Conventional convective solutions through the recirculation of indoor air (i.e., ducted or wall-mounted fan-coil or split systems) have been found to be the most robust. They are generally simple to design, install and commission, have a lower capital cost than radiant systems, and power can be modulated to deal with peak loads. They are less comfortable than radiant systems. Split systems using refrigerant distribution offer greater dehumidification power (due to lower refrigerant sink temperatures than water) with a faster response than fan-coils and water distribution. However, the Glower Warming Potential (GWP) of the refrigerants and risk of leaks from on-site manipulation is an important consideration. Figure 10 shows monitored data for ducted split system. Temperatures outside the extended comfort range are during hours when the home was not occupied, and the clients report a high level of thermal comfort.

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Figure 10: System 6, Cardedeu, ducted split units

Thermodynamic analysis of an electric underfloor heating system

The article presents the results of a thermodynamic simulation study, comparing Wood Plastic Composite (WPC) floorboards with ceramic and stoneware floor tiles, heated with an electric underfloor heating system, for both dry and wet assemblies.

Thermodynamic analysis of an electric underfloor heating system

The article presents the results of a thermodynamic simulation study, comparing Wood Plastic Composite (WPC) floorboards with ceramic and stoneware floor tiles, heated with an electric underfloor heating system, for both dry and wet assemblies. The different floor finishes have been modelled in a multi residential building, in Madrid (Spain) climate, using the DesignBuilder-EnergyPlus simulation tool. 

The objective of the study is to analyse the dynamic thermal response of each kind of floor finish, comparing heating energy consumption, peak heating power, floor surface temperature and indoor air temperature. 

Floor types

The Table below shows the different types of floor systems that were modelled:

Figure 1: Floor types and variants included in the analysis

Calculation model

The DesignBuilder tool with the EnergyPlus thermodynamic calculation engine has been used for the simulations.

A multi-residential 4 storey building has been modelled, consisting of 4 dwellings per floor, each with ~ 86 m2 of net floor area, and 342.1 m2 of total heated floor area. The second floor of the building has been modelled for the study, with the floors above and below modelled as adiabatic (they are assumed to be occupied and heated, with the same occupancy and internal heat gain conditions).

Figure 2: Render of the complete building
Figure 3: Render of the calculation model, 2nd floor

The exterior walls are cavity wall with a 14 cm perforated brick outer layer, 5 cm air-void, 6 cm of thermal insulation, and 9 cm of interior hollow brick layer, with 1cm of gypsum plaster (U = 0,39 W/m2·K). The dwellings have aluminium window frames with thermal breaks (Uf = 3,6 W/m2·K) and air-filled double glazing (Ug = 2,9 W/m2·K & g = 69%). The dwelling have mechanical ventilation with an average air change rate of 0.63 ach, with sensible heat recovery that has a efficiency rate of η = 70 %. For dwellings, air infiltration has been calculated as N50 = 5/h, converted to atmospheric pressure and applied to each zone according to its exposed area. Common areas, as the staircase, air infiltration have been modelled with 1 ach of air infiltration.

The energy consumption of all 4 homes on the second floor has been analysed, with a detailed analysis of Room 1 (oriented to the southwest).

Electric radiant floor system

An electric radiant floor system has been modelled. Heating mats with the following nominal power capacities were simulated under each type of flooring:

  • Wood Plastic Composite (WPC) floor (direct system): 75 W per linear metre
  • Wood Plastic Composite (WPC), with self-levelling mortar screed: 116 W per linear metre
  • Stoneware/ceramic floor, with self-levelling mortar screed & gypsum plasterboards: 116 W per linear metre

The radiant floor power for each home and for Room 1 is shown in the following table. The radiant floor has been modelled as “ZoneHVAC: Low Temperature Radiant: Electric” and inserted into DesignBuilder using an EnergyPlus script.

Figure 4: Radiant floor capacity per dwelling

Temperature setpoints

The heating setpoints are those indicated in Annex D “Operational conditions and usage profiles” of the Spanish Building Regulations CTE DB HE 2019:

  • Main setpoint: 20 ºC (07:00 – 22:59)
  • Secondary setpoint: 17 ºC

Results

The 3 periods shown in the following table have been analysed:

Figure 5: Analysis periods

The following parameters have been analysed:

  • Heating consumption [kWh]
  • Maximum capacity of the radiant floor heating mat [kW]
  • Floor temperature [ºC]
  • Indoor air temperature[ºC]

Dry installation: thermal transmittance, thermal resistance, and internal heat capacity

The Figures below show the radiant floor capacity, total thermal transmittance (according to ISO 69446), thermal resistance of the materials on top of the radiant floor heating mat, and the internal heat capacity of the materials above the radiant floor (according to ISO 13786), for each type of floor, for a dry installation.

Figure 6: Total thermal transmittance, thermal resistance above radiant floor & internal heat capacity per area unit above the radiant heating mat, dry installation
Figure 7: Total thermal transmittance, thermal resistance above radiant floor & internal heat capacity per area unit above the radiant heating mat, dry installation

Wet installation: thermal transmittance, thermal resistance, and internal heat capacity

The following graph and table show the radiant floor capacity, the total thermal transmittance (according to ISO 69446), the thermal resistance of the materials above the radiant floor heating mat, and the internal heat capacity of the materials above the radiant floor (according to ISO 13786), of each flooring type, for a wet installation.

Figure 8: Total thermal transmittance, thermal resistance above radiant floor & internal heat capacity per area unit above the radiant heating mat, wet installation
Figure 9: Total thermal transmittance, thermal resistance above radiant floor & internal heat capacity per area unit above the radiant heating mat, dry installation

Dry installation: 2nd floor, heating consumption, 1st October – 31st March

The Table and the Figure below show the results of heating energy consumption for each type of floor, for a dry installation.

Figure 10: Heating consumption results, dry installation, 1st October – 31st March

The results indicate that the heating consumption of floors 2.1 Stoneware and 2.2 Ceramic with double gypsum fibreboards is 20% higher than in 1.1 WPC (direct system).

Floor consumption 3.1 Stoneware and 3.2 Ceramic with 1 dry gypsum fibreboard, is 5% and 4% higher than 1.1 WPC. These differences fall within the margin of uncertainty in the calculations (around 10%).

Figure 11: Heating consumption results, dry installation, 1st October – 31st March

Wet installation: 2nd floor: heating consumption, October 1st – March 1st

The next table and graph show heating consumption results for each floor type, with wet installation.

Figure 12: Heating consumption results, wet installation, 1 October – 31 March

The results indicate that heating consumption of 4.1 Stoneware and 4.2 Ceramic floors with self-levelling mortar screed, are 10% and 9% lower respectively than 1.2 WPC with self-leveling mortar screed. These differences fall within the margin of uncertainty in the calculations (around 10%).

Figure 13: Heating consumption results, wet installation, 1st October – 31st March

Dry installation: Bedroom 1, floor & indoor air temperatures, radiant floor power, and solar gains, January 14th

The evolution of radiant heating mat capacity is shown in the Figures below, together with solar gains, floor surface temperature, and indoor air temperature, during the day of January 14th, for each floor type, for dry installation.

Additionally, the maximum capacity of the radiant heating mat, the time at which maximum capacity occurs, and the maximum floor surface temperature (before the effects of solar radiation) are shown.

The heating setpoint and setback temperatures (20 ºC from 7:00 – 23:00 and 17 ºC the rest of the day) determine when the radiant floor is turned on or off. Solar gains provoke sudden rises in indoor air and floor surface temperatures when the radiant floor is off.

Figure 14: 1.1 WPC, winter day, radiant floor capacity, solar gains, floor temp. & air temp.
Figure 15: 2.1 Stoneware, 2 gypsum fibreboards, winter day, radiant floor capacity, solar gains, floor temp. & air temp.
Figure 16: 2.2 Ceramic, 2 gypsum fibreboards, winter day, radiant floor capacity, solar gains, floor temp. & air temp.
Figure 17: 3.1 Stoneware, 1 gypsum fibreboard, winter day, radiant floor capacity, solar gains, floor temp. & air temp.
Figure 18: 3.2 Ceramic, 1 gypsum fibreboard, winter day, radiant floor capacity, solar gains, floor temp. & air temp.
Figure 19: All floors, dry installation, winter day, radiant floor capacity, solar gains, floor temp. & air temp.
Figure 20: Radiant floor max. capacity, max. floor temp. and time delay, dry installation

The table and graphs above show that the delay between radiant heating mat’s maximum capacity and maximum floor temperatures, is around 4 hours for the 1.1 WPC, approximately 6 hours for stoneware floor and ceramic floor with 2 gypsum fiberboards, and approximately 5 hours with 1 gypsum fiberboard.

This is mainly because the thermal resistance and thermal capacity of the 1.1 WPC (direct system) is lower than with the stoneware and ceramic floors with gypsum fiberboards, therefore takes less time to warm up and transmit heat to the room.

Wet installation: Bedroom 1, floor & indoor air temperatures, radiant floor power, and solar gains, January 14th

The graphs below show the evolution of the radiant heating mat power capacity, solar gains, floor surface temperature, and indoor air temperature, during January 14th, for each floor type, for a wet installation.

The radiant heating mat maximum capacity, the time at which maximum capacity occurs, and the maximum floor surface temperature (before the effects of solar radiation) are shown. For the 1.2 WPC, the maximum floor temperature takes place at 12:00 due to the heat emitted by the radiant heating mat; from that time on, the increase in floor temperature is due to solar gains.

Figure 21: 1.2 WPC with self-levelling mortar screed, winter day, radiant floor capacity, solar gains, floor temp. & air temp.
Figure 22: 4.1 Stoneware, self-levelling mortar screed, winter day, radiant floor capacity, solar gains, floor temp. & air temp.
Figure 23: 4.2 Ceramic, self-levelling mortar screed, winter day, radiant floor capacity, solar gains, floor temp. & air temp.
Figure 24: All floors, wet installation, winter day, radiant floor capacity, solar gains, floor temp. & air temp.
Figure 25: Radiant floor max. capacity, max. floor temp. and time delay, wet installation

The above graphs and table indicate the time delay between the radiant floor’s maximum capacity and the floors maximum temperature, for the WPC, stoneware, and ceramic floor with self-leveling mortar screed, is around 5 hours in all three cases.

Although the heat capacity of the materials above, the radiant floor of floor types 4.1 and 4.2 is far greater than the 1.2 WPC, the thermal resistance of these materials is much lower, so the dynamic response and heating consumption is similar.

Conclusion

The results of the dry installations, indicate that the Wood Plastic Composite flooring has lower energy consumption (between 4% and 20%) and a slightly faster thermal response. In the case of floors with wet installation, the results indicate that the Wood Plastic Composite flooring has a slightly higher energy consumption (between 9% and 10%) and a thermal response similar to the other floor types analyzed. In both cases, given the margin of uncertainty of the calculation, the difference is minimal.