5 ways to a successful heat pump deployment – #2 Optimise hydraulic circuits for low return temperatures

Cooling down, to crank up the pay-off

Heat pump or not, low return temperatures are a must-have for any well-performing heating system. Sadly, this is often not the case, especially where installations are old or have been updated/adapted over time. 

As we already discussed in our first blog, in non-domestic installations, hybrid heat pump/boiler system designs are likely to make the most sense – both from a CAPEX and efficiencypoint of view. However, to achieve maximum contribution from a heat pump in a hybrid installation, sufficiently low return temperatures and maximum differential between flow and return temperatures (delta T) are vital. That last part is why it is crucial to ensure this area of the heating installation is handled correctly in the design and planning stage of a project, particularly if you are retrofitting a heat pump into an existing installation. Poor hydraulic design and imbalances across your existing installation, are usually the culprit of high return temperatures under partial load conditions.

Why is all this important you ask?The benefit of low return temperatures is compounded for heat pump installations. Since operating temperatures are so critical to the heat pump efficiency, having lower return temperatures makes it possible for heat pumps to produce more thermal energy within their optimal efficiency window. Let’s paint a picture, shall we? Imagine a hybrid heat pump/boiler installation witha return temperature of 40°C. In such an installation, the heat pump should ideally be installed in the return flow and operate as a “pre-heat” for the boiler. This way, the boiler will only fire if the system water temperatures can’t be met by the heat pump alone.

With a lower return temperature, the installation will be able to run more efficiently and will allow a higher total contribution from the heat pump.  For example, if the maximum flow temperature from the heat pump is, say, 55⁰C and the return temperature is already 50⁰C, there’s not a lot the heat pump is going to contribute!

Of course, higher temperature output heat pumps are available – and that’s a discussion for a later blog.  But even high temperature CO₂ heat pumps work best with a wide system deltaT.  So tackling the causes of high return temperatures are crucial for optimal system performance.

And of course, there are other advantages to lowering return temperatures, including lower pump energy consumption – in fact reductions of 80% or more are often possible; lower system heat losses; and improved performance of any associated condensing boiler plant.

That’s why dynamic simulation is such a great thing. By identifying the causes of high return temperatures, we can design them out of the system, and contrary to popular belief, at a low investment cost.

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Solution software to the rescue

Successful implementation of low carbon heat solutions, require coordination and expertise. To address these challenges, Hysopt has developed tools and personal dedication to analyse challenges and implementing solutions that benefit both your company and our environment.  

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