Improve efficiency: Weather compensation based on effective temperature

As we all know, heat pumps are more efficient when the flow temperature is low.

I’m running a large heat pump with over-sized radiators in a 200-year old house.

A common feature of modern heat pumps is weather compensation. Often this will be a “curve” which provides a high flow temperature when it’s cold outside and a lower flow temperature when it’s warmer outside. Some even have multiple points on the curve so it’s not linear!

My control algorithm uses a simple straight line at the moment.

However, I’ve also included a weather station so now I can work out the effective outside temperature rather than the measured temperature. That’s the temperature I use for my weather compensation.

I was motivated to do this when storm Ciara made the house a bit cooler that desired and I wanted the machines to sort it out.

Interestingly in the Danfoss video they refer to the windiness meaning you’d want to alter the curve but they had a human altering the curve instead of the machines.

I’m hoping to use Emoncms to provide a pluggable way to include the effective temperature in my algorithm.

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Here’s a graph showing how the outside temp and the desired flow temp varied. It takes a bit of reading, but you can hopefully make out that the high points of the flow temp go up when it’s cold and down when it’s warmer outside.

For example, it was cold on Feb 5th so the flow was 42, but it was warm on the 9th so the desired flow was around 35 degrees.

You’ll be wondering whey they don’t track each other more precisely. It’s because I only set the desired flow temperature when the heat pump is active.