Optimising heat pump system efficiency with control valves
Maintaining the correct temperature differential (DT) in a heat system is essential for the operation of any heat pump.
Valves are an essential part of that system – playing a vital role in controlling both temperature and flow at many points.
Here, we’ll cover two key uses of control valves that we’ve found to work well in many applications. But first…
Why is DT so important?
DT, also known as Delta T, is the difference between the flow and return temperatures.
Essentially, flow temperature is the temperature that your heat pump heats your water to before it gets sent to your emitters (usually, your radiators).
Meanwhile, the return temperature is the temperature at which that water returns to your heat pump after flowing through your emitters.
Every refrigerant has an optimal DT – meaning it has flow and return temperatures at which it’s able to operate most efficiently.
Heat pumps generate heat at a temperature much closer to the flow temperature than boilers. And because the DT of the refrigerant is critical to both efficiency and internal pressure management control of system, DT is vital to success.
For example, CO2 (R744) is most efficient with a 70C flow and 30C return. While some CO2 heat pumps can certainly tolerate higher return temperatures, this will compromise their efficiency.
With that in mind, heat pump designs should be predicated on achieving a refrigerant’s optimal temperatures.
This will not only enhance heat pump efficiency but it will also, in doing so, allow end users to maximise carbon savings and minimise energy costs.
Luckily, control valves can play an important role in both flow control and temperature management – two factors that are key to maintaining optimal DT. Which brings us onto…
Managing return temperatures
Pressure Independent Control Valves (PICVs) integrate the functions of a differential pressure regulator, a control valve, and a flow limiter into a single unit.
PICVs may be used in many parts of the system. For example: on each radiator, on a heating circuit, or on the main return to the heat pump.
But in systems utilising natural refrigerant heat pumps, PICVs are particularly advantageous.
This is because of the huge role they can play in managing return temperatures.
1. Stable flow control
PICVs automatically adjust to maintain a constant flow rate regardless of variations in system pressure.
This is critical in ensuring that heat transfer and energy extraction are consistent, which stabilises the return temperatures of LTHW systems.
2. Prevention of overheating
By maintaining precise flow limits, correct control of PICVs prevents excessive heating of the return water.
This is essential for CO2 heat pumps, which require a 30°C return temperature to operate within their efficient supercritical range.
3. Dynamic adjustment
PICVs respond dynamically to changes in demand from signals via the control panel, such as fluctuating heating requirements across zones.
This adaptability ensures that the return water temperature remains within design limits.
PICVs should be specified to be fast-acting in order to react in sufficient time to give good control.
Temperature control
3-port diverter valves play a critical role in maintaining optimal return temperatures in systems that use propane refrigerant heat pumps.
They do this by ensuring the heat pump operates within its design parameters.
Here’s what their role in temperature control strategy looks like.
- The valve maintains a consistent return temperature set point, depending on the system design requirements
- If the return temperature falls below the set point, the valve modulates to divert flow from the flow line, mixing it with the return water to raise the temperature
- This strategy ensures the heat pump maintains the required DT between flow and return temperatures, which is critical for achieving efficient heat transfer and system stability
In this way, 3-port diverter valves can safeguard your heat pump from inefficiencies or operational issues that could arise from improper temperature differentials.
Plus, by maintaining the DT, they can support the heat pump in achieving its target flow temperature, which ensures reliable and consistent heating delivery.
Let us worry about control valves for you
As you can see, these tiny pieces of kit have a big role to play in natural refrigerant heat pumps. And their role is highly technical.
With that in mind, it’s worth noting that any technical advice provided here is for informational purposes only.
While we strive to ensure the accuracy and reliability of the information provided, it isn’t intended to be a substitute for professional advice or services tailored to specific circumstances.
Rather, that’s what our heat pump system designers are here for!
Our system designers have a wealth of experience and will be happy to design a complete heating system that works perfectly for you and your building – from the heat pump to the control valves.
Just get in touch for bespoke advice and guidance.