Why high-temperature heat pumps are NOT the answer for heat decarbonisation in non-domestic buildings

As the role for heat decarbonisation becomes ever more critical for building owners and the public sector to achieve net-zero carbon targets, low carbon electricity means heat pumps now have the potential to deliver immediate carbon savings. 

BUT for existing non-domestic buildings, heat pumps are not a like for like replacement for gas boilers and best practice system design will be essential if they are to be deployed successfully.

What’s more in commercial and non-residential applications – ranging from offices, to university campuses; schools, town halls and hospitals - “hybrid” designs, integrating heat pumps and gas boilers together will very likely be a common approach.

Myth #1: heat pumps aren't suitable for existing buildings

The addition of heat pumps - which are of course perform most effectively at lower operating temperatures - is often thought to be prohibitive for “high” temperature heating installations.

Furthermore, the “spark gap” between the unit costs of gas and electricity needed to run heat pumps means the cost of delivered heat will mean unacceptable ongoing running costs.

Myth #2: high-temperature heat pumps are the only answer

It’s a fact of course that heat pumps perform most efficiently at lower operating temperatures. And while “high temperature” heat pump models are available, proper system design which takes a “whole system approach” can mean that the additional investment and operational costs of inefficient high-temperature units can be avoided.

The whole system approach

So with the combination of high price differences between electricity and gas; and heating systems in existing buildings being designed around high operating temperatures, how is it possible for heat pump systems to deliver BOTH low carbon AND low running costs?

There are two elements in particular that are often missed.

Firstly, plant, pipework and radiators in nearly all existing heating systems are already over-sized, due to the limitation of the existing design process. It’s possible therefore to take advantage of this over-sizing and reduce primary system temperatures to a level suitable for heat pumps to operate efficiently. 

We've recently been working with a major client to look at the deployment of heat pumps across a range of existing non-domestic buildings. High-temperature heat pumps had already been proposed, however using Hysopt digital modelling and dynamic simulation, it's been possible to demonstrate very clearly that peak load operating temperatures could be reduced from 80°C to 60°C; and average operating temperatures throughout the year (weather compensated) of less than 50°C. Meaning conventional "low temperature" units could be used; and operating in a window of relatively high efficiency compared to more expensive "high temperature" versions.

This is without having to replace any heat emitters and simply taking advantage of system oversizing that was already in place, making the installation significantly more cost-effective from both an upfront investment and ongoing operational cost point of view.

These improvements mean it is possible to increase the seasonal heat pump efficiency (SCoP) from below 200% (original high-temperature heat pump design) to over 390%, delivering carbon savings of over 80% compared with the original gas boiler installation, while also mitigating the risk of increases in annual energy bills.

Sizing for hybrid installations

Secondly, running heat pumps in a hybrid mode, by allowing existing gas boilers to contribute during peak hours also enables the deployment of heat pumps to be more cost-effective – again from both an investment and operational cost perspective.

In our example case, Hysopt was able to demonstrate that heat pumps sized to provide just 50% of the peak thermal load would provide 99% of the annual thermal energy contribution, with back up boilers providing just 1% when flow temperatures needed to be raised a little higher to meet the demands on a few days of each year.

Using heat pumps in this way; and deploying only low-temperature models reduced the capital investment costs by 60% compared to the original “high temperature” proposal. Plus the increased seasonal efficiency of 3.9, combined with smart, flexible tariffs and appropriately sized energy storage enabled heat pumps to be added with a negligible increase in annual running costs compared with the previous gas boiler installation. 

Bringing transparency at the design stage

Critical to the success of projects such as this is the transparency over system performance that digital modelling tools, such as the Hysopt project software are able to provide.

Heating (and cooling) systems in larger buildings and where multiple heat technologies are being deployed are far too complex to be designed and simulated without software. At Hysopt, we prove this on a daily basis using our CIBSE award-winning Digital Twin software to help building owners and design engineers deliver cost, energy and carbon savings by hydraulic optimisation of heating and cooling installations, for both new build and existing buildings.

In short, a digital model of an HVAC installation gives energy managers and building owners real insight as to how their system works and allows objective comparisons between the impacts of multiple future design options. In this way, digital twins can help organizations to make the right technical and financial investment decisions, reduce risk and increase the prospects of delivering against targets by objectively quantifying ‘performance’ at the design stage.

Want to find out more...?

Our recent e-guide on key ingredients for the successful deployment of heat pumps into non-domestic buildings is available to download and will explain more.

Or why not join our upcoming webinar on 25th February, where together with Newcastle City Council, we will explain more about HOW and WHY heat pumps DON'T need to operate at high temperatures in existing buildings. Register here

www.hysopt.com

[email protected] 07719 902067