Which fan coil units are ideal for systems with LTHW below 65/60°C?
Heat pump ready fan coil units (FCUs) are ideal for systems with low temperature hot water (LTHW) below 65/60°C. These units have been designed to work with the lower-grade heat from heat pumps, low-temperature district heat networks (DHNs) and other low-temperature sources, to meet both the heating and cooling requirements of conditioned spaces.
Fan coil units that are normally 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. If they are connected to a supply from a heat pump, they need to be able to cope with the temperature drop in the LTHW and still deliver the required level of heating efficiently.
The fan coil units need to extract more energy from the lower temperature water to transfer it and deliver warm air than they would 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 scenario for specifiers.
This is why heat pump-ready fan coil units are an ideal match for heat pump systems and low temp DHNs. They can deliver the heat output from LTHW as low as 45/35°C using a low-temperature ready coil in an energy-efficient compact unit that reduces both operational and embodied carbon.
What design challenges do heat pump ready FCUs need to overcome to work with heat pumps?
Heat pump-ready fan coil units need to overcome key design challenges if they are to work with low-temperature heat sources.
1. Increase the volume of air passing over the coil
This could be achieved by increasing the fan speed. However, this also increases the noise output. Therefore, larger fans would be needed, thus increasing the size of the unit and its energy consumption.
2. Increase the size of the fan coil
Fitting a larger fan coil unit would increase the heating capability as it has a larger coil and surface area; however, this would add to the embodied carbon contribution on the project.
3. An additional heating coil
This is a scenario where the size of the unit and its embodied carbon increase by featuring additional coil, or coils. The efficiency decreases. Whilst these options can be viable workarounds, these challenges can be overcome through specification of heat pump ready FCUs.
How are heat pump ready FCUs designed to work so well with LTHW?
Heat pump ready fan coil units overcome the challenges of working with the lower grade heat by a clever redesign of the heat exchanger coil in the FCU. The surface area of the coil is increased and uses a contra-flow design to maximise heat transfer efficiency. It enables sufficient energy to be extracted from LTHW at existing air flows. There is no need for a larger fan or for a secondary heating coil to boost heat output. This reduces the embodied carbon of the heat pump ready FCU.
The coil is also re-circuited to reduce pressure drops and lower system resistance. This decreases the work required by the pump, increasing the heat pump ready FCU energy efficiency. The redesign of the coil does not affect the cooling performance of the heat pump ready FCU, and its acoustic performance is maintained.
The heat pump ready FCU is effective for systems that use fossil fuels or setups with higher LTHW supply temperatures. Therefore, it can be installed on new commercial buildings where fossil fuels are initially being specified to help to future-proof them in preparation for eventual change to renewable energy sources such as ASHPs.
Where can I find more information about heat pump ready FCUs
Ability has years of experience in designing and manufacturing fan coil units. We have developed an innovative heat pump ready fan coil unit that is ideal for use with renewables running with LTHW below 65/60°C such as ASHPs. It is now installed in multiple projects where it delivers reliable, efficient heating and cooling and can bring project savings in both embodied and operational carbon.
If you have a query about heat pump ready FCUs or a project related question, please contact our experienced technical team, who will be happy to help.
Troy Chambers
