Speeding up the learning curve for integration
Integrating renewables with conventional heating technologies is not just a good way of cutting energy consumption and emissions, it is also a great way to satisfy local planning officials while enabling a wider range of end users to benefit from the latest technology, says David Pepper of Lochinvar.
Equipment that generates or uses renewable energy is no longer a novelty, but the industry is still on a fairly steep learning curve, especially in terms of integrating such products with conventional boilers and water heaters. However, the experience gained as more of these systems go in is starting to pay back handsomely.
An integrated or hybrid system is not just a good way of keeping capital spending relatively low while still delivering substantial savings in running costs — it is also a cost-effective way to meet the requirements of local planning departments. It also means some end clients who might previously have considered renewables to be beyond their budget can now afford a renewable element that helps them satisfy planning requirements and meet their corporate social responsibility (CSR) obligations.
Such an integrated system would include boilers and water heaters in combination with a renewable technology, with thermal stores being installed as part of the integration. This is proving to be an increasingly popular way for a project team to build in the degree of flexibility needed to meet varying levels of heating and hot-water demand in a growing range of commercial buildings.
The refinement of heat-pump technology so that features previously only available in large multi-stage compressors are now included in smaller models is also making a huge difference. Add this to the fact that air-source heat pumps (ASHPs) remain eligible for Government subsidy under the Renewable Heat Incentive (RHI) programme, and the financial case is persuasive.
The industry is also making greater use of multi-valent systems where energy is gathered from a number of separate sources — including solar thermal, heat pumps and condensing gas-fired boilers and/or water heaters.
In such a system, the use of a suitably flexible thermal store becomes the critical element. A plate heat exchanger connects the heat pump to the thermal store, and it is important that the system is sized and managed correctly to ensure the non-renewable plant only runs when required — so minimising fossil-fuel use. The thermal store acts as a large, low-resistance header that can accept heat from up to three sources. This smooths out the system capacity to maximise efficiency. It also prevents legionella risk because it avoids the need to store domestic hot water for long periods.
However, to deliver this kind of solution requires a robust control strategy and a sensible commissioning period to ensure the system components work in the right sequence. It should be set up to ensure the renewables are the first to respond to any call for heating and hot water, with gas-fired boilers acting as back-up and firing only during periods of particularly high demand.
Commissioning will only be effective if there is proper consultation with the building manager/end user to establish likely patterns of occupant behaviour and the resulting hot-water and heating usage. It is also crucial to have integration in the supply chain so everyone adopts a suitably joined-up approach. In many cases, manufacturers are being called on to provide the know-how to knit the delivery process together because of their specialist knowledge.
One example where all the parts of the integration jigsaw came together was the Callywhite Care Home in Derbyshire, which accommodates 39 residents and has been carefully designed for the elderly and particularly those living with dementia. It features an integrated heating system including a gas absorption heat pump. Hot water is provided separately by gas-fired condensing water heaters.
Initially solar photovoltaic (PV) panels were specified to meet local authority requirements for renewables and attract feed-in tariff (FiT) payments to the owner. However, on closer inspection, it was decided that an Optimus gas absorption heat pump (GAHP) supplied by Lochinvar was a more appropriate choice for this type of project.
Rather than the ‘tick-box’ approach taken on many designs simply to achieve planning consent, the Callywhite project team took all the relevant factors into account and recognised that the integrated system approach would be more appropriate and would deliver a better long-term result for the home and its residents.
As an added bonus, the Optimus met planning requirements at a considerably lower cost than the solar PV — even when the FiT payments were taken into account.
The heat pump also helped the team comply with dementia care design guidelines, which favours low-temperature underfloor heating, avoiding the use of radiators on safety grounds. Optimus GAHP has a gas utilisation efficiency (GUE) of 152% at a flow temperature of 50°C when ambient air is 7°C and is, therefore, well-suited to this type of application.
It was important that the contractor, Martin Dixon Ltd, was able to work closely with the equipment manufacturer to engineer the integrated system, which involves the GAHP providing heated water to a thermal store serving the underfloor heating system. This means the two CPM gas-fired, fully condensing, stainless-steel boilers are only used as back-up and to provide extra heating capacity on very cold winter days, so keeping energy and carbon emissions to a minimum.
Callywhite is a classic example of a project where the technologies deployed offer a number of operating benefits in their own right, but it is the extra investment in early planning and design work to get the integration right that makes all the difference to the long-term performance.
David Pepper is managing director of Lochinvar.