ELECTRIC.IE • The Magazine & Website for the Irish Electrical Industry • 45 Industry News How do we fit heat pumps in apartment blocks? One of the objections to towards mandating heat pumps as we phase out fossil fuels is that they are difficult to fit in multi-occupancy dwellings. Typically, in this country, we see air source heat pumps that are designed for outdoor installation, whilst ground source units that are installed indoors require land for a collector loop – either a sizeable horizontal loop or the more compact, but more expensive, vertical borehole. Neither of these scenarios is immediately obviously ideal for a block of city centre flats without gardens, that want individual bills for each unit. In truth there are quite a few solutions to this problem. The first, and perhaps most obvious, group of products to meet this need is units for indoor installation that do not require a collector loop; air source heat pumps that can be installed indoors. These come in a number of flavours. Exhaust Air Heat Pumps (EAHPs) are installed as inside units, with heat extracted from air inside the building and fresh air drawn in to replace it. They combine MVHR (mechanical ventilation with heat recovery) with a heat pump circuit to boost the amount of heat for use in heating and hot water. The downside with these is the amount of ducting required to make the system work, making them less than ideal for retrofit situations, where it can be difficult, expensive, and time consuming to fit, potentially requiring existing residents to vacate the property. To work well these really need sizeable apartments (as large volumes of air must be cycled and this otherwise means high air throughput which can feel drafty) and low loss heat losses. So although effective, Head of Technical at STIEBEL ELTRON John Felgate explores the challenge. EAHP’s can be difficult to size appropriately. For this reason, we have always seen low demand for this product and don’t currently carry a model in our range, though we have in the past. Alternatively, there are indoor units which draw air from outside for heat extraction. These require only the ducting for the heat pump through an external wall – much as a boiler may have a flue, although the vents are larger. They can be for heating and hot water or hot water only as a supplement to electric room heating. Room to place the heat pump is obviously a constraint as you need a fairly large cupboard on an outside wall to make this work; an allowance best made during the design stage of a new building. But in the instance that you have that space, these are a great solution. Again, demand for these in the UK has yet to take off as developers and architects grapple with understanding the requirements to make it possible early enough in a project’s evolution, and we supply them only for bulk orders such as whole apartment blocks as we don’t hold them in the UK as standard stock for individual call off. My preferred solution for apartments is actually a shared collector loop with small ground source heat pumps in each unit so that bills are individualized. The very best performing system we have tracked via our internet service gateway is actually this kind of set up, offering really phenomenal SCOP. In this instance the system has boreholes on communal land. One of the advantages of this design is that as the refrigerant rises through the building to the flats on upper floors it gains heat from solar gain and the fabric of the building. This means that whilst the ground floor can have a source temperature of 10 degrees, it can be 15 or even 18 degrees by the time it reaches the top floor, leading to excellent efficiencies. Ground source heat pumps have the advantage of being quieter in operation that air source and so noise from the units in the apartment is minimal in this scenario. The piping required for the refrigerant can also usually be run through service risers that exist even in older buildings making this a good solution for retrofit. Another variation on this solution, where there is insufficient land even for boreholes, is what is called an ambient loop. In these systems a set of air source heat pumps installed on a roof can be used as “collector loop” for ground source heat pumps in each apartment. This approach has been adopted by a number of local authorities for social housing blocks, and is also efficient and effective with the same advantages of quiet operation and individual bills, though obviously requiring some extra communal plant. John Felgate
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