Heat pump ready fan coil units (FCUs) are well suited for systems with low temperature hot water (LTHW) below 65/60°C. These Ability by Dimplex FCUs have been specifically developed to operate effectively with the lower grade heat produced by heat pumps, low temperature district heat networks (DHNs) and other low temperature energy sources, while still meeting the heating and cooling demands of conditioned spaces.
Fan coil units that are supplied with hot water from fossil fuel boilers are not ideal for low temperature sources, as they are designed to run with LTHW flow temperatures at 65/60°C or higher. When connected to a heat pump supply, they must still be capable of delivering the required heat output despite the lower water temperatures available.
In these situations, the FCU must extract more energy from lower temperature water to provide the same level of warm air delivery that would normally be achieved with higher temperature hot water. This can lead to larger output fan coil units being specified or ancillary heating coils being added to units, increasing their size. Such solutions use more energy and introduce more embodied carbon into the building. In a building that is using a renewable heat source, introducing additional carbon into the project is not an ideal outcome for specifiers.
This is why heat pump ready fan coil units provide an effective solution for heat pump systems and low temperature DHNs. They are capable of delivering heat output from LTHW temperatures as low as 45/35°C, using a low temperature ready coil within a compact, energy efficient unit that helps reduce both operational and embodied carbon.
What design challenges do heat pump ready fan coil units need to overcome to work with heat pumps?
Fan coil units intended to operate with heat pumps must address several design challenges associated with low temperature heat sources.
Increase the volume of air passing over the coil. One option is to increase the fan speed to move more air across the coil. However, this typically leads to higher noise levels. Larger fans may therefore be required, which increases both the size of the unit and its energy consumption.
Increase the size of the fan coil. A larger fan coil unit can improve heating performance because it provides a larger coil and greater heat transfer surface area. However, this also increases the embodied carbon contribution of the unit within the overall project.
Additional heating coil. Another option is to incorporate one or more supplementary heating coils within the FCU. While this can increase heat output, it also increases the size of the unit, raises embodied carbon and reduces overall system efficiency.
Although these approaches can provide workarounds, specifying heat pump ready FCUs provides a more effective and efficient solution.
How are heat pump ready FCUs designed to work with LTHW?
Heat pump ready fan coil units address the challenges associated with lower grade heat through a redesigned heat exchanger coil within the FCU.
The coil surface area is increased and arranged using a contra-flow design to maximise heat transfer efficiency. This design allows sufficient energy to be extracted from LTHW while maintaining existing air flow rates. As a result, there is no requirement for a larger fan or secondary heating coil to increase output, helping to reduce the embodied carbon of the heat pump ready FCU. The coil is also re-circuited to minimise pressure drops and reduce system resistance. This lowers the workload on the circulating pump and improves the overall energy efficiency of the system.
Importantly, the coil redesign does not compromise the cooling performance of the heat pump ready FCU and the acoustic characteristics of the unit remain unchanged.
Heat pump ready FCUs can also operate effectively with systems using fossil fuels or higher LTHW supply temperatures. This means they can be specified in new commercial buildings where fossil fuel systems are initially installed, helping to future-proof the building for a later transition to renewable energy sources such as air source heat pumps (ASHPs).
Where can I find more information about heat pump ready FCUs
Ability by Dimplex has extensive experience in the design and manufacture of fan coil units. The design team developed an innovative heat pump ready FCU specifically intended for use with renewable heat sources operating with LTHW below 65/60°C, such as ASHPs.
These units are already installed across a range of projects, where they deliver reliable and efficient heating and cooling while supporting reductions in both embodied and operational carbon.
If you have a query regarding heat pump ready FCUs or a project-specific question, contact the Ability technical team, who will be pleased to assist.
