Passive housing andthe concept of thepassive solar househave been aroundfor many years. InIreland we have manyexamples of whatwas known as thepassive solar house.It was quite differ-

ent to the Passivhaus concept developedand made successful by Wolfgang Feistand the Passivhaus Institut in Germany.

The passive solar house in IrelandThe passive solar house, particularly inIreland, did not feature the attention toU-value, air-tightness and cold bridgingthat is now prevalent in low energy housing.There were several reasons for this. We

had not developed the methods of build-ing which were readily and economicallyavailable to achieve very low U-values inpractice. Some wall constructions weredesigned to give low U-values but in real-ity did not do so in practice due to siteconstruction problems. Similarly, triple-glazed windows were not economicallyavailable through Irish suppliers. It wasfound difficult to build houses to levels

Passivhausor passive solar house?

A PASSIVE SOLAR HOUSE CONCEPT DESIGNEDFOR IRELANDFew concepts in sustainable design have caught on like the passive house. Since the con-struction of the first passive house in Germany in 1990, an estimated 15 to 20,000 houseshave been built to what is arguably the world’s leading low energy building standard. Draw-ing from his experience in sustainable building since the early 1980s, Bill Quigley of NuTechRenewables posits an alternative approach.

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of air-tightness that were deemed neces-sary for low energy housing, and elimi-nating thermal bridging was difficult giventhe methods of construction and the methodsof analysis available at the time. It’s fairto say that the Irish construction indus-try simply was not ready to be forcedinto the highly specialised techniques toachieve the U-values and air-tightness re-quired and also, and probably most im-portantly, there simply was not the willto deliver a near ‘zero-energy’ house.

This gave rise to an extraordinary situa-tion, where the ‘low energy house’ in practicecould cost considerably more to run thanthe actual design amount as is illustratedin figure 1. If the actual heat losses aredoubled – which could well be the casebecause of poorly installed insulation,lack of air-tightness and serious thermalbridging – then the running costs tripledover the design value as the amount ofsolar gain remained approximately the same.

With this knowledge and with the growingnumber of architects and engineers interestedin this area of low energy house technol-ogy, a number of examples were built.

Probably the first serious example of a passivesolar house in Ireland was the Garristownhouse in County Dublin, built between1979 and 1980. The concept design wasby the well known engineer and special-ist in thermodynamics John Cash, for whomthe house was actually being built. Dun-can Stewart was the architect and othercolleagues of John and Duncan in DIT werealso involved in various aspects of thehouse design. Huge efforts were made toensure that this house achieved its de-sign values and indeed it was such a suc-cess that it sparked considerable interestin this area. As can be seen from the photothis reasonably well insulated house fea-tured a massive solar wall of some 110 m2.

Another example of a passive solar housebuilt a little later than the Garristown housewas the Knocklyon solar house, whichwas built and monitored between 1983and 1989. This house featured an earlyversion of a solar heating and ventilationsystem which eventually evolved intoNuTech’s Sunwarm system. This earlysystem had 40m2 (gross) of air solar col-lectors. In reality this was a passive solarhouse with an active solar feature. Thecollector array fed energy into the heat-ing and ventilating system and into thedomestic hot water system. The wall in-sulation in this house – an early versionof bonded bead – proved troublesomeand had to be replaced by blown fibre-glass. Difficulties were also experiencedin attaining a high degree of air-tightness.Many different systems were tried andtested in this house including air solarcollectors, phase change material heat storageand solar assisted heat pump technology,to name a few. A huge amount of infor-mation was gathered by way of the datamonitoring system, the results of whichwere reported to the energy directorateof the European Commission.

The Knocklyon project in particular led theway to a simplified passive solar houseconcept developed by Mark Forkin and Iat NuTech Renewables. This concept canachieve the same results as a more ex-pensive-to-build passive house. Detailsof this system together with a compari-son will be given later in this article.

Figure 1: effects on energy usage with increased heat loss characteristic

(above) Ireland’s first example of a passive solar house in Garristown, County Dublin, fea-tured a solar wall of some 110m2; (below) the Knocklyon solar house featured a solar heat-ing and ventilation system; (opposite, top) a clay / straw passive house in Tattendorf,Austria; (opposite, bottom) a NuTech designed passive solar house built with KTF’s inno-vative timber frame system

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The passive house conceptThe passive house concept as put forwardby the Passivhaus Institut is a very excit-ing development and is of its time, as thefabric elements and the systems involvedare now fully developed and widely available.

The basic requirements are:

• The house will use not more than15 kWh/m2 per year of deliveredenergy for space heating.

• The house will have a specific annual heating load of less than10 W/m2. This does take into accountthe heat gains by way of solar gains through the windows andthe internal heat gains due to occupancy. Hence, it should be noted that this is a different figureto the energy required to meet the specific heat loss characteristicof a house for a given temperaturedifference.

• The air-tightness of the house willbe such that the air infiltration rate will be less than 0.6 air changesper hour at 50 Pa.

• Thermal bridging will be reducedto a minimum.

• A heat recovery ventilation systemis used to supply the necessaryair for ventilation. It must have an efficiency of more than 75 per cent. The system will supplyat least 0.3 ACH of fresh air.

• A solar water heating system shouldbe used. Typically, a 3m2 EvacuatedTube Array with a 300 litre domestichot water cylinder will suffice.

By these means the necessity for a fullprimary central heating system are negated.It is generally sufficient to add any extraenergy by way of energy delivered froman internal wood pellet stove normallyplaced in the fireplace of the house, or byway of a small heat pump which is extractingenergy out of the extracted air which hasalready gone across the HRV unit. The designof this unit is catered for in the PassiveHouse Planning Package (PHPP) software.PHPP is a most useful and comprehensivetool to aid the designer in arriving at asatisfactory solution based on all of the abovepoints. To use this package will requiremost designers to undertake a certain amountof training. To date courses are being of-fered by SEI/REIO and by Nicer Training.

Typically, to satisfy the above criteria thefabric U-values must be less than or equalto the following1:

The following points should be givencareful consideration:

• An air infiltration level of less than0.6 ACH at 50 Pa is very low indeed.It represents an actual infiltrationrate at normal pressure of less than 0.03 ACH. It would be our view that with only 0.3 ACH of fresh air being delivered by wayof the HRV system, considerationwould have to given to the humiditylevel in the house in winter as it could drop to very low levels

indeed – a figure of 35 per cent relative humidity at 20oC.

• The draft Part F of building regulationscall for a fresh air requirement of 0.3 litres of fresh air per secondper m2 of floor area. This must betaken into account and supersedesany other requirements as set out in the PHPP.

• At this level of air-tightness, greatcare would be required in the fittingand use of an internal wood pelletstove to ensure that there was no depressurisation in the roomit is sited. Also, the stove wouldhave to be room sealed – in otherwords its combustion air wouldhave to come from outside – as it should in all low energy houses.

• The difficulty in achieving this level of air-tightness should notbe underestimated.

• If the temperature of the house should drop due to non-occupancyin winter, then the power requiredin the heating system would have to be greater than 1200 W in orderthat the house would heat-up ina short time as power will be required to overcome the thermalresponse/thermal mass of the house. Alternatively, homeownersshould be told to leave the heating on even when they are away as it will use so little energyin the first place.

• To save costs some passive housedesigners use a direct acting electric heater in the air duct toprovide back-up heating. It shouldbe remembered that when this is taken into account in SEI’s DEAPcalculation a severe penalty is incurred as the use of electricalenergy is multiplied by a factorof 2.7. Very often it can move the rating of the house on the BERscale from being an A2 house toa B2 rating.

• Large areas of south-facing andindeed east- and west-facing glazingshould be given careful consideration.The possibility of overheating due to solar gains through thesewindows must be considered and appropriate steps taken.

• It is vitally important that the fabric thermal performance levelsare achieved in practice. If there is only a 1200 W heater tocater for deficiencies and if the actual heat losses were somewhathigher than the design, then it would be disastrous for the comfortlevels experienced by the home

owner and the running costs wouldescalate accordingly.

There is no doubt that if all of the criteriaare adhered to rigidly then a low energyhouse will result. Comfort levels will besatisfactory and running costs will be verylow. However, it is important that all ofthe above points are taken into consider-ation by the designer and the builder.

The NuTech passive solar house conceptThe NuTech passive solar house conceptis a little different. It was devised originallyby Mark Forkin and this author out of thedesign and systems used in the originalpassive solar house in Knocklyon. All ofthe technologies developed have beenrigorously tested over the past 20 years.

In essence, the U-values arrived at are alittle less strict in certain circumstancesover the PHI values to ensure cost breaksare achieved and then this is compensatedfor by way of a larger solar array of evac-uated tubes delivering energy into the HRVsystem even in cloudy weather (hence thereason for using evacuated tubes over flatplate collectors). The thinking is that asinsulation levels get higher and higher itis a clear case of diminishing returns whichare, as mentioned, offset by the amountof energy delivered to heating by way ofthe solar array. NuTech are in full agree-ment that high levels of air-tightness areessential. The reduction in thermal bridgingis also vitally important as this has anenormous effect on the overall heat losscharacteristic (W/K) of the house.

Typically, the NuTech requirements forthe fabric U-values must be less than orequal to the following:1

As can be seen there are some essentialdifferences to the typical PHI requirements.The external wall U-value is raised to0.16 W/m2K as it can be achieved in tim-ber frame with a reasonably sized studwhich then has internal insulation fixedto reduce the effect of thermal bridging.The window U-value is raised to 1.2 W/m2Kas it then allows the use of well designeddouble glazing rather than the more ex-pensive triple glazing unit. The level ofair infiltration has been raised to 1.0 ACH

U-Value (W/m2K)Ground floor 0.12External wall 0.13Roof 0.14Windows and doors 0.80

U-Value (W/m2K)Ground floor 0.12External wall 0.16Roof 0.14Windows and doors 1.20

Infiltration level 1.0 ACH at 50Pa

Figure 2: a schematic of the NuTech integrated solar heating and HRV unit in apassive solar house

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at 50 Pa – a difficult but more achievabletarget which also helps reduce construc-tion costs. Finally the energy from at leasta 6m2 evacuated tube solar array is inte-grated into the HRV system, thus solarheated air is being circulated to all roomswithin the house even in dull weather. Theheat generator, whether it is an internalwood pellet boiler or an air to water heatpump is also integrated into this system.This fully integrated system is controlledby way of the NuTech intelligent renew-able energy system (IRES) controller.

As regards thermal bridging, systems havebeen developed with the timber framecompany KTF Ltd., such that the amountof thermal bridging is hugely reduced byway of the insulation systems and partic-ularly by way of details around the win-dows and doors. As mentioned above, thisis vitally important. It is worth rememberingthat if the thermal bridging factor in theDEAP analysis is 0.08 W/m2K then the U-value for all of the elements is increasedby this amount. A wall U-value of 0.16W/m2K therefore becomes 0.24 W/m2K inthe overall calculation. It is that serious.

This passive solar house system has many strongfeatures. It has reasonably low U-values forall of the fabric items, and is tested to achieveless than 1.0 ACH at 50 Pa. It integrates theenergy from the solar array into the HRVsystem, and similarly integrates energy fromthe back-up boiler (internal wood pelletor heat pump) into the HRV system.

There is also a facility to have filtered re-circulated air within the system therebyallowing 5 kW to 10 kW of heat to be dis-tributed around the house, based on thesize of house. This greatly improves thethermal response of the back-up heatingsystem should it be required. The venti-lation system is designed to meet the re-quirements of the draft Part F of the Irishbuilding regulations.

A unique feature is that during periodsof higher levels of solar radiation, morefresh air is brought in by way of the HRVsystem to ventilate the house to a higherlevel than required by the building regu-lations to maintain freshness within thehouse. This can be done as it is using thesolar array to its optimum level and thehouse is being either heated or ventilatedat a zero energy penalty.

A higher percentage of the domestic hotwater will be achieved by this system thanwith the smaller array on the normal passivehouse because there is twice the area ofsolar collector. The NuTech passive solarhouse is designed to achieve an A2 ratingon SEI’s BER scale.

A significant point with the NuTech passivesolar house is that SEI’s DEAP calculationmethod allows the designer to take into accountthe energy from the solar array that is beingtransferred to reduce the energy demandfor space heating. This improves the BERrating of the NuTech passive solar houseand aids the achievement of an A2 rating.

A comparison of the two concepts In carrying out a comparison of a typical200m2 house the various parameters wereinputted into the DEAP calculation methodsuch that both systems should give ahouse design with an equal BER rating.

The parameters were as follows:

Both houses are designed to have the sameBER of 46 kWh/m2/yr and are thereforeachieving an A2 rating. However, the NuTechpassive solar house offers a number ofcost and performance benefits. The ex-ternal wall will be considerably cheaperto build and the windows being doubleas opposed to triple-glazed may be farcheaper. The back-up heating can deliverfar more energy by way of the integratedheating system and can therefore copewith a far faster thermal response. Morefresh air is delivered when there is moresolar radiation available thereby givingincreased fresh air at no energy penalty.

It is suggested also that rather than havingvery large areas of south-facing glazingwhich may cause problems of over-heat-ing in summer, that a larger area of solarcollector can achieve the same result withoutthe over-heating problem.

ConclusionsThe Passivhaus Institut design and the NuTechpassive solar house both offer systems thatwill perform very well in Ireland. Bothsystems will deliver high levels of com-fort at exceptionally low running costs. Itis proposed that the NuTech passive solarhouse will achieve the same BER rating ata lower capital cost.

1SEI’s Renewable Energy Information Office haspublished Passive homes: Guidelines for the designand construction of passive house dwellings inIreland, including specific U-value requirementsfor building Irish passive housing. Visithttp://tinyurl.com/passivhausireland to accessa PDF of the document.

NuTech passive solar house passive house standard

DEAP calculation 46 kWh/m2/yr 46 kWh/m2/yrIndicative BER A2 A2Floor area 200 m2 200m2

Wall (U-value) 0.16 W/m2K 0.13 W/m2KWindows & doors 1.20 W/m2K 0.80 W/m2KGround floor 0.12 W/m2K 0.12 W/m2KRoof 0.14 W/m2K 0.14 W/m2KThermal bridging Equal EqualSolar array 6m2 Thermomax delivering 3m2 Thermomax to domestic

energy to domestic hot water hot water onlyand to the integrated HRV and heating system

(below) In the NuTech system, the energy from the solar panels is integrated into the HRVsystem (top) circulating warm air to all rooms within the house even in dull weather (mid-dle) a NuTech/KTF passive solar house under construction at a Fingal County Council so-cial housing scheme at Oldtown