ENERGY SAVING EQUIPMENT


different heat pump systems. AM16 is focused on the use of heat pumps to provide heating, although the use of heat pumps for cooling is also mentioned - see box Heat Pumps for Cooling. The manual deals with the design and optimisation of multi-unit heat pump systems to provide heat for space and domestic hot water (DHW) heating. As such, it has been structured in line with the recommended heat pump design process.


The document starts with advice on measures to reduce heat demand at the point of use. The aim is to minimise both heating and DHW demands in order to minimise the size of the heat pump to make it smaller, more affordable and more efficient to run. Essentially, these reduction measures are about following best practice in order to reduce space heating loads. Measures to reduce space heating typically include: improving building envelope airtightness; minimising heat losses through the building fabric, including the elimination of thermal bridges; and using heat recovery on the ventilation system to reduce fresh air loads. Good design of sufficient and well controlled


ventilation is essential for both occupant well-being and low carbon solutions. With appropriate technology and effective management it is possible to create an indoor environment with sufficient outside air to reduce viral transmission which also supports strategies to reduce carbon emissions and reach net zero. For DHW systems, measures can include the use of low-flow taps and insulating pipework. A heat pump for a multi-residential development may provide all or part of the energy for space heating and domestic hot water. To size the heat pump the building's thermal demands in terms of peak load, demand profile and temperature must be understood.


For space heating in multi-unit residential schemes both peak demand and demand profile may need to be calculated for the various scales: at room and dwelling level to allow the heat emitters, heat interface units or in-home heat pumps to be sized; at building level, to allow communal heating systems to be determined; and at development level in the case of district heating networks with plant in a centralised energy centre. As well as the peak demand and the demand profile, the temperature required for the low temperature hot water (LTHW) at the emitter and DHW at the fitting should be established. These temperatures will dictate the flow


temperature required from the heat pump. When it comes to selecting a unit, there are a variety of heat pump technologies available, the most common of which are air source heat pumps (ASHPs) and water source heat pumps. Attention needs to be given to the performance envelope of a heat pump, which is the range of temperatures at the condenser and evaporator at which the heat pump can operate.


For example, ASHPs using current


technology are effective and capable of producing water at a maximum of 55C at -5C ambient temperature. To achieve higher water temperatures at these ambient conditions alternative refrigerants may need to be considered, or a series of heat pumps may need to be configured to boost the flow temperature. There is a section on domestic hot water temperatures (DHW), to consider the impact on heat pump efficiency and the design DHW temperature requirements. The document includes a detailed chapter on


sizing a heat pump system, including sizing a heat pump to meet a proportion of peak load. Sizing a heat pump to meet part of the peak load and using an alternative heat source, such as direct electric, can save space and capital cost when peak demand is only for a limited number of hours each year. Once sized, the location of the heat pump also needs to be considered. Heat pump systems generally take up more space than gas boilers of the same capacity, particularly if the system includes ancillary plant such as buffer vessels. Condenser location may also be restricted by noise and airflow concerns. AM16 has a very detailed chapter on system optimisation. This includes advice on the impact temperature has on a unit's efficiency. For example, the lower flow and return temperatures serving emitters, such as radiators, will affect their size, cost and embodied carbon. The document includes example correction factors for radiators operating at lower temperatures. For retrofit applications where the existing


LTHW flow temperatures are higher than 55°C, the document suggests that interventions, such as implementing energy efficiency measures to reduce demand, will be required along with increasing the radiator sizes. Once installed, it is vital that the refrigeration plant and associated systems are properly commissioned. AM16 references various CIBSE Commissioning Codes and includes a list of key recommendations to successfully commission a refrigeration


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system. With the system up and running, routine maintenance should be planned to ensure its longevity and efficient operation. Adequate space must be provided for operators to undertake this task safely. The expected lifespan of a heat pump is 10-15 years, although manufacturers may indicate longer lifespans for well-maintained units. AM16 also addresses the issue of user


guidance, which is important for a technology that is very different to traditional fossil fuel heating systems. In addition, a series of case studies have been included in the document to showcase the successful application of heat pumps in both new and existing multi- residential projects.


Heat pumps for cooling


Although Application Manual 16 is focused on the use of heat pumps to provide heating; the use of heat pumps to provide cooling is included, although it is not covered in detail because in the UK residential buildings should aim to design out the requirement for active cooling through natural ventilation by following industry standards for thermal comfort, such as CIBSE TM52 and TM59.


Heat pumps can be used to provide active cooling in situations where residents are particularly vulnerable, or where local noise or air quality issues prevent residents from managing overheating through opening windows. Active cooling can also form part of the brief for high-end residential developments where there is a market expectation for air conditioning. Space cooling demands should be calculated in a similar manner to space heating demands. Space cooling loads in non-residential areas in mixed-use developments should be included if there is the potential to improve the system efficiency through heat sharing. To optimise the heat pump system in order to take advantage of heat sharing, the cooling load profile needs to be understood. The designer can then see both the relative annual heating and cooling energy demand and the periods of coincident demand and size the system appropriately.


CIBSE AM16: Heat pump installations in multi- unit residential buildings 2021, brings together best practice and industry-wide advice. The manual was authored by Arup with the support of the NHBC Foundation. It is available as a download: X www.cibse.org/knowledge


www.acr-news.com • January 2022 35


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