Gas-driven heat pumps have the potential to slash energy bills by a third on retrofit projects – but, as with all renewable technologies, only if well designed, sized, installed, controlled and commissioned. As the industry debates the level of involvement required from manufacturers to raise efficiencies, Mike Hefford, Head of Renewable Technologies at Remeha Commercial, provides an insight into a two-year project where manufacturers were given full scope to design, install and monitor a bespoke-designed hybrid heating and hot water system at a care home near Banbury.
For legislative, financial and environmental reasons, renewable technology, often supported by gas-fired condensing boilers, is increasingly specified as the prime source of energy for heating and water provision on both new build and refurbishment projects. Yet, recent projects have highlighted the frequent failure of these sophisticated hybrid solutions to deliver the predicted energy and carbon savings due to the renewable equipment underperforming or failing to operate at all.
One suggestion currently being proposed is that manufacturers, who are arguably best placed to advise on their products’ installation and operation, should be given greater scope in system design to help avoid the performance gap between anticipated and actual energy usage. On projects where the high efficiency figure quoted by manufacturers on their product is not achieved, the cause invariably stems from a failure to adhere to good system design and control rather than to a problem with the product itself. This can be a cause of great frustration for manufacturers, for as soon as a heating product is released, the manufacturer effectively relinquishes control over it, despite being responsible for it whilst it remains under warranty.
A recent refurbishment scheme for a care home in Banbury provided Remeha Commercial with the perfect opportunity to analyse the impact of greater manufacturer involvement on achieving the anticipated efficiencies from a heating system. Lake House, one of 70 care homes run by the not-for-profit care provider The Orders of St John Care Trust (OSJCT), offers private rooms for 43 residents and communal facilities. When the existing boilers began to fail, Graham Hipwell, the Facilities Manager at OSJCT, was particularly interested in upgrading the heating system with renewable energy equipment as the Trust looks to reduce its carbon footprint and utility bills. There were two main considerations when recommending a new system, the first being reliability, due to the vulnerable nature of many of the residents, and the second the high demand for heating and hot water. To meet these requirements, Remeha proposed installing Fusion Hybrid, our recently developed hybrid heating and hot water system that combines gas absorption heat pumps (GAHPs) and condensing boilers with a BMS control for high performance.
Gas absorption heat pumps are gaining increasing support as an adaptable renewable solution to heating, offering enhanced environmental and financial benefits for building operators due to their use of gas rather than electricity to drive the heat pump and of an ammonia/water working fluid rather than CFCs as the refrigerant. Furthermore, Lake House was particularly suited to being heated by GAHPs as the existing heating system was designed for a maximum flow temperature of 42⁰C to ensure the low temperature surface for the radiators and pipework that is required by a care home.
For Remeha, this was the perfect opportunity to pilot our new technology: it would enable us, its manufacturers, to gain thorough understanding of the exact capability of the system through hands-on experience, arming us with the knowledge of how to achieve the highest efficiencies from the heat pumps that would support best practice on future applications. The OSJCT would also benefit hugely as the arrangement would effectively ensure optimum operation of the new heating and hot water system and consequently maximum energy and carbon savings.
Remeha proposed installing Fusion Hybrid at Lake House as a turnkey project. Not only would we be responsible for the specifying, installation and commissioning of the project, but we included a two-year monitoring period in the agreement, following which time Remeha would train staff at the OSJCT to operate and manage the system. For data purposes, we installed pulsed heat and gas meters to provide valuable information on the proven efficiencies achievable in a real life scenario.
The problems that arise with renewable equipment, particularly sophisticated hybrid systems that combine renewable and traditional heating, are generally due to a lack of in-depth knowledge and understanding within the industry of this sophisticated technology. In essence, there are five key steps to follow when working with renewable technology: size right, design right, install right, control right and commission right. At Lake House, the Remeha engineers followed the five key steps from the outset for a textbook installation. The care home was previously heated by three condensing boilers with a total output of 180kW. To meet the required heating and hot water demand, three 35kW GAHPs were installed on a mounted plinth in a yard outside the boiler house as the primary source of heat generation. The GAHPs directly heat water within a 1000 litre twin coil buffer vessel to 50⁰C and preheat the cold water feed. Heat is transferred to the heating system by a coil in the cylinder and blended with the return water to reach the required flow temperature. This is controlled according to heat load and can be as low as 30⁰C. The lead heat pump is rotated every 200 hours to ensure good operation. The system also includes two 45kW gas condensing boilers installed in cascade to provide support when required, although to date this has proved minimal due to the efficiency of the GAHPs. In addition, the GAHPs are used to preheat incoming mains water before it is topped by direct-fired water heaters which have an output of 48kW.
Good control is critical to the effective operation of hybrid systems, enabling individual components and the overall system to achieve their maximum potential. Fusion Hybrid uses a specially-configured, scalable BMS to integrate the two high-efficiency technologies and match more accurately the heating and hot water requirements of the building. It is important that controls are straightforward and easy to use. With the Fusion Hybrid, a 7-inch touchscreen panel called the Remeha Touch provides a display of the performance data of all the components with clear options for adjustments to ensure optimum operational efficiencies. The system can also be monitored and controlled remotely which certainly provided useful in this project.
The transition to the new system was carried out in just half a day with the two condensing boilers installed first in order to maintain heating and hot water throughout the care home for the benefit of the residents.
So what have we learnt from the experience at Lake House? Firstly, the project has demonstrated the enormous energy saving potential of gas absorption heat pumps and of the Fusion Hybrid system in particular. Prior to the Lake House experience, we had anticipated achieving efficiencies of between 120 and 130 per cent. This proved to be a conservative estimate as data from the pulsed gas and heat meters indicates that the GAHPs are delivering a seasonal efficiency of 140 per cent (NB efficiency is based on the net calorific value for gas absorption heat pumps). The heat pumps are also providing around 90 to 95 per cent of the heating for the care home. In terms of savings, a comparison of energy use from December 2013 and December 2014, reveals a 27 per cent reduction in gas consumption following the installation of the Fusion Hybrid system. This means financial payback for the OSJCT in four to five years – or sooner still when gas-driven heat pumps become eligible for RHI funding, which is expected to be announced later this year.
Would we do it differently next time? Overall, this was a highly successful project and the system is continuing to deliver the desired results. However, ideally, there would have been an allocation in the budget to upgrade the water heaters. In terms of controls, zoned control was also not an option. That said, the occupancy at Lake House stays fairly stable as it is a care home, and the extra valves and pumps that zoned control requires would have brought higher capital costs and higher running costs for the nursing home. We carried out careful commissioning as this step is crucial to achieving maximum performance and yet often the part that is skimped when projects run over budget. The hydraulic commissioning confirmed that everything was working as we had hoped, with just a few minor tweaks required to the controls for the gas absorption heat pumps.
This project has confirmed to us the value of consulting manufacturers on hybrid and renewable technology to achieve maximum thermal efficiencies. The detailed information that manufacturers hold on their product, from how it works to how best to size it, combine it with other equipment and integrate it within an existing system, can be critical in avoiding an energy performance gap from heating. Whilst the monitoring process that we carried out at Lake House might not be commonplace, manufacturers have already stepped up, offering turnkey biomass projects and assuming more responsibility in the sizing, design and installation of CHP to support the project team and see their products operate at their optimum level. Manufacturers can also support the project team by providing realistic efficiencies on their product rather than headline efficiencies achieved in laboratory conditions. The data from this project, for example, has contributed to the accurate performance table we are able to provide to assist consultants in calculating the outputs and efficiencies of this hybrid system to suit their own projects. This greater involvement and sharing of knowledge is, of course, at the heart of what will become our industry’s new way of working. Ultimately, it is the greater collaboration amongst our fellow professionals, supported by initiatives like Building Information Modelling, rather than an allocation of responsibilities that will enable us to achieve the potential savings from renewable technologies, helping prevent the dreaded performance gap and raising the performance of our buildings.
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