An emerging option within the UK heating and hot water market is the hybrid system. Hybrid systems use two fuels, contributing towards cleaner operations while maintaining efficient performance.
Why hybrid and not full electric? There may be certain technical or financial constraints that prohibit full electric heating and or hot water systems from being installed in every non-domestic building. According to government statistics there are around 2.13 million non-domestic buildings in the UK. In cities these buildings are generally clustered together so space is a premium, and installing large capacity heat pumps to satisfy the full building demand may not be viable.
The electrical loading on the building may also prevent going full electric, or the building owner may not have the funds available to switch to a full electric system either on a capital and/ or operational expenditure. Rather than not doing anything, hybrid systems can be a good way to start a building’s decarbonisation journey.
Hybrid systems consist of a combination of traditional fuel sources like natural gas, oil or LPG, and a renewable technology such as solar thermal or a heat pump. Hybrid systems optimise factors such as outside temperature, current energy prices, property heating and DHW demand. For smart domestic hot water systems such as continuous flow water heaters used with heat pumps, the renewable heat generator provides the base load as the water heaters “top up” the temperature.
UNDERSTANDING COMPONENTS
A hybrid system is comprised of a number of features, components, technologies and fuels. The heat pump is the renewable backbone of the system. Most hybrid systems use air source heat pumps (ASHPs) due to their ease of installation and affordability.
Ground source heat pumps (GSHPs) are also viable for specific applications, particularly in commercial settings.
A high efficiency condensing gas boiler or water heater serves as the backup heat source. Modern condensing water heaters are designed to extract as much heat as possible from combustion gases, increasing energy efficiency.
When solar thermal collectors are included, they can contribute heat to the system directly or to a buffer tank. This heat can then be drawn upon before the system calls for either the heat pump, gas boiler and water heaters, making it more energy efficient.
The control unit or smart thermostat is the ‘brain’ of the hybrid system, responsible for deciding which heat source to use based on real time conditions. Many units are integrated with weather compensation and predictive algorithms.
A buffer tank or hot water cylinder is an optional component, but one recommended for systems that provide domestic hot water (DHW). The buffer tank helps to smooth out demand fluctuations and improve efficiency. Other cylinders can include buffers for minimum water content and for additional hot water demand.
Then, sensors and meters measure temperature, flow rates and energy consumption, feeding data back to the control system to enable automated switching.
OFFERING MULTIPLE BENEFITS
Having two separate fuels in a single system offers a range of benefits. The first is financial: as electrical costs are higher than natural gas, using a system that accepts both renewable electricity and traditional fuel sources could make costs lower and more manageable compared to an all-electric system. From a capital expenditure perspective, the cost will be lower than a full electric system creating lower whole-life costs.
In terms of operational performance, combining two technologies ensures energy efficiency while supporting operational consistency. A hybrid system will preferably incorporate the heat pump or solar thermal technology during mild weather, then use the other appliance during periods of cold weather. This optimises the strengths of each technology in different weather conditions, while adding a combustion-based water heating technology will boost the renewable base load to ensure DHW performance.
A further benefit for the end-user is that the lifecycles of both technologies are lengthened. As each technology does not have to apply full effort to satisfy demand, component and overall system longevity will be increased due to a lessening of required workload.
Hybrid systems offer a practical route for net zero objectives to be accomplished. They introduce customers to alternative and clean energies while maintaining control over energy costs by still relying on conventional and more cost-effective methods of energy usage.
Consultants, contractors, specifiers and installers are advised to consider using manufacturers and suppliers of decarbonising technology with proven records of successful installations of hybrid systems that equip locations with the ability to reduce costs and emissions.
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