Heat Pumps For New Higher Education Buildings
For new builds, consultants are already specifying a greater electrical load to account for the additional power demands to support a mixture of heat pumps and direct electric afterheat necessary to meet the higher water temperatures and volume demands exhibited in higher education projects. Due to their relative ease of installation compared to ground source systems, we will focus on Air Source Heat Pumps or ASHPs. New domestic hot water (DHW) systems will predominantly follow this model, taking advantage of heat pump performance efficiencies to create a hybrid approach to deliver pre-heating for as much as 75% of the water in a direct electric system. Able to draw and transfer thermal energy from air, under the right circumstances ASHPs represent an efficient way to significantly reduce the carbon emissions of a building and with no gas to the building, no local generation of NOₓ and no flue to install this clearly has its advantages.
However, with ASHPs offering greater efficiencies in low-temperature systems, the high-temperature demands of DHW for higher education applications can be a challenge. High temperatures need greater compression of the refrigerant, requiring more electrical input which results in lower efficiency or Coefficient of Performance (COP).
When analysing the value of an ASHP in terms of reducing CO₂ emissions the carbon intensity figures from SAP10 should be used and advantage of ASHPs is that their performance is greater than 100% as they extract additional energy from outside of the building’s metered systems. This gives significant carbon savings but, when describing the efficiency of an ASHP, working flow water temperatures of 35°C are often cited. It needs to be recognised that this temperature is insufficient for higher education applications. Even if a college or universtiy building has achieved Passivhaus standards, and this remains a rarity, 35°C is not going to be hot enough to safely provide DHW. Achieving 60°C in a calorifier is a basic requirement for a commercial DHW system, but means the working flow temperature from the ASHP would need to be at least 65°C. As well as struggling to achieve these temperatures year-round in the UK, the COP drops very low meaning you lose the value of deploying ASHPs. A calculated working flow of 55°C is certainly attainable from current generation ASHPs and this is why when designing commercial DHW systems it is preferable to use a hybrid approach that uses the ASHP as preheat and combines it with either gas-fired or more preferably electric immersion top up to achieve the required hot water temperature.
Attention also needs to be given to the Ecodesign established European temperature zones when assessing the suitability of a heat pump to serve a building’s DHW heating load. For most of the UK the relevant defined temperature zone is ‘average’, where the annual reference temperature for the ASHP’s Seasonal Coefficient of Performance, or SCOP, is -10°C. For some Southern and Western UK regions, the ‘warmer’ Ecodesign temperature zone can be applied for modelling, where the lowest the reference temperature will only fall to 2°C. These differing temperature regions can have a significant impact on the SCOP therefore it is important to ensuring the values entered into an assessment are both relevant and accurate for the installation. Incidentally, the SCOP of an ASHP is a far better overall gauge of the year-round efficiency as opposed to COP. While COP figures are often cited in technical literature, you must remember that these represent very specific climatic conditions that may only occur for a moment in time.
Commercial DHW applications using heat pumps are going to be complex and, compared to gas-fired alternatives, are going to have higher up-front costs. Designing the system for peak efficiency, and therefore sustainability, is a must to help offset this additional capital investment when compared to traditional gas-fired systems. With 50 years of specialist experience in creating bespoke commercial DHW systems, Adveco is well-positioned to support such projects with a wide range of air source heat pumps, indirect tanks and electric immersions. Under the right circumstances, such as new builds with a high degree of insulation, ASHPs represent an efficient way to significantly reduce the carbon emissions of higher education buildings. As the cost of grid electricity closes on that of gas, ongoing savings garnered from operating a hybrid ASHP based system, plus the reduction in CO₂ emissions makes the technology a truly attractive prospect for the latest building projects on higher education campus. New innovations in heat pump technology and refrigerants this coming year will further enhance the advantages of the technology cementing it position as a truly viable alternative for the provision of commercial-grade hot water.