How do we achieve the electrification of heat in apartment blocks?

Heat pumps as a solution for flats

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 obviously ideal for a block of city centre flats without gardens, that want individual bills for each unit.

n 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, 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 fairly large cupboards near 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.

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 ground collector can also be run through service risers that exist even in older buildings making this a good solution for retrofit.  

Graph showing performance of a heat pump in a flat from a shared borehole

the blue line at the top shows the room temperaturewhich hovers around a comfortable 21.5 DegC.

The yellow line at the bottom shows the chilly outside air temperature which is consistently below -5 DegC.

The red line in the middle shows the speed of the compressor which modulates around 25Hz which is it's most efficient zone.  The spikes up to 45Hz are when the heat pump heat up the domestic hot water tank.

In short, this is a picture of a heat pump working hard in cold weather and maintaining a highly efficient pattern of operation.

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.  

Electric room heating and instant and point of use water heaters

Electric space and water heating solutions provide a viable alternative to heat pump technology in new build multi occupancy residential buildings.  There are some great reasons to choose electricity as a fuel for heating apartments in the UK. Not least of which their low capital cost and maintenance requirements.   

In new build bocks, where heat demand is low, panel heaters are a simple choice. In apartments with just a shower we often pair these with single phase instananeous water heaters. This hits a sweet spot for developers, keeping costs to a minimum and saving the space needed for a hot water storage tank. Meanwhile bills are kept low by the high efficiency of this kind of water heating and the advanced controls on our room heaters.

For apartments with baths, 3 phase instantaneous water heaters can be used for great effect and the additional electrical infrastructure required can be cost neutral when compared to space savings from central tanks and the ease of installation.

For PRS or student accomodation, the low maintenance of all-electric solutions is also a great boon when compared to fossil fuel options. 

Conclusion: electric heat for decarbonisation

The Government are targeting net-zero carbon emissions by 2050, electric space and water heating, as a low carbon solution, will have a pivotal role to play in the decarbonisation of heat in the UK.  We can work with specifiers and SAP assessors to design electric system that are clean, efficient and compliant with the latest building regulations.