Heating and hot water

Heating and hot water

A Passivhaus building can in theory be heated via the fresh air supply – that is after it is heated to around 50°C. This idea of doing away with a conventional heat distribution system helped define the Passivhaus standard, but isn’t necessarily the best choice. Any heating system can be used – radiators, underfloor heating, split system air conditioning, wood burning stove and you can use a gas boiler, a heat pump or district heating. Direct electricity for both heating and hot water is not normally possible because electricity’s high primary energy factor means this usually exceeds the Passivhaus primary energy limit of 120kWh/(m2.a).

Hot water often uses more energy than heating in a Passivhaus so it pays to concentrate on designing an efficient system. Use the DHW sheet in PHPP at an early stage in design, since the losses here are included in the summer overheating...

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Gas boilers are the default heat source in the UK and can easily be used in a Passivhaus. Combi boilers provide hot water on demand, and as such have high kW output so tend to need additional radiator capacity to buffer this. System boilers...

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Air heating is the defining method for Passivhaus, in theory minimising costs. In practice there are a lot of reasons for not using air heating:

• A particular room’s demand for heat and fresh air are rarely in balance – bedrooms need...

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PHPP works out an overall heat load, in terms of watts and W/m2 . This gives a continuous heat load – ie, assuming the heating is on 24/7, and is aimed at seeing if heating via the air is possible. The numbers are fi nely balanced, which may be...

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It makes sense to think of the heating system as primarily providing hot water, plus heating as and when needed. The efficiency of the hot water system, ie, minimising losses from storage and distribution, is significant both in terms of energy...

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Don't
Spend a lot of money on a biomass boiler or bore hole heat pump system
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Expect that a 100% electric heating and hot water system will comply with the primary energy limit for Passivhaus certification.
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Do
Fill in the PHPP DHW section before looking at overheating.
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Chose heat pumps that provide good hot water performance rather than heating
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Put the hot water storage (or combi) in the same area
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Arrange the layout to keep hot water outlets in a reasonably compact form
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Consider radiators as your first option
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Use a cheap and simple heating system – the investment belongs in the building fabric
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