Heating systems


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Taking the heat out of decarbonising existing buildings


A


s the drive to decarbonise heat in buildings accelerates, the favoured route for many building owners will likely be to replace


existing gas boilers with electric heat pumps. However, even with the most modern high temperature air source heat pumps (HT ASHPs), decarbonising harder-to-heat buildings remains a huge challenge for our industry. Swapping out boilers for heat pumps can be done, but a full understanding of the existing heating system is absolutely essential. And this is where partnering with heating and hot water experts can help.


Fabric fi rst


Designing with energy effi ciency in mind is crucial. So where possible, a fabric fi rst approach should always be the fi rst step. The purpose of fabric upgrades is twofold: to


reduce the size of the heating plant and the amount of power it requires, and to lower operating costs by reducing the heat losses from the building through air infi ltration or the building fabric. The main reason that heat pumps are tied in with this approach, though, is due to fl ow temperatures. As we know, air source heat pumps (ASHPs) operate most effi ciently at lower fl ow temperatures. Without fabric improvements, emitters may need to be re- sized to give the right heat output. However, if heat demand can be reduced through fabric upgrades, the equation should balance itself out. It would appear to be a logical, straightforward


approach. But what happens in older or even listed buildings where it is simply not feasible to improve the fabric, either due to cost implications or to heritage status?


Swapping boilers for heat pumps


In such a scenario, a hybrid heat pump solution is nearly always a fast, effi cient and aff ordable answer. This is because even a modestly sized heat pump will enable a large portion of the heat in the building to be decarbonised. As such, a hybrid system can be a quick win solution, delivering immediate sustainability improvements while overcoming key challenges such as budget and risk. If the client brief is to move straight to full


electrifi cation of heat, however, one consideration might be high temperature ASHPs like our new


14 June 2024


R290 (propane) Auriga+ ASHP which can deliver up to 80°C fl ow temperature. But here’s the caveat. For existing heating systems designed around 82/71°C or potentially 80/60°C operating temperatures, this will be at the very top end of the performance envelope for even the most modern of HT ASHPs. It should also be noted that higher temperatures come at a cost to effi ciency. Additionally, most heat pumps prefer to operate in the 5-10°C ∆T range, making a straight swap on 80/60°C circuits challenging.


Investigative engineering


Realistically, designing the most eff ective replacement heat pump design will require investigative engineering to understand how the building lives and breathes all year round. To do this, we need to know the actual heating demand at a system circuit level, not just the total installed capacity of the current heat generation plant. Building a thermal profi le of real usage from


existing gas meters or by installing ultrasonic meters, will enable a clearer understanding of the building.


Optioneering


With this real measured data, it is then possible for heat experts like Baxi to engineer diff erent solutions. Optioneering allows us to work out how much of an impact a solution will make, enabling clients and designers to make the best choice within the project requirements and constraints. For example, off setting heat loss ineffi ciencies by having on-site electricity generation through equipment such as photovoltaics (PV).


Targeting Net Zero carbon in existing buildings with heat pumps while ensuring comfort and cost-effi cient operation, is a huge challenge. Ryan Kirkwood, engineering solutions manager at Baxi, discusses the importance of fabric fi rst options, investigative engineering and optioneering for optimal performance and value


Left: Ryan Kirkwood, engineering solutions manager at Baxi


“Realistically, designing the most eff ective replacement heat pump design will require investigative engineering to understand how the building lives and breathes all year round.”


Ensuring best value and performance


In short, well-designed hybrid systems and major replacement projects require a signifi cant amount of investigation and measured data to understand the system fully. Fabric options should always be a fi rst consideration when decarbonising asset heat and will typically yield a higher effi ciency overall than a high temperature heat pump system. Partnering with heating and hot water experts will help to make the process simpler. Working together, we can arrive at clear, concise and pragmatic solutions that deliver optimal immediate and longer-term results. By following this approach, we can support our customers’ decarbonisation journey and ensure that the right decision is reached in every case.


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