A weekend away…

Click image for a larger version. The view from Winchelsea village is splendid, and in my opinion, all the better for the views of Camber Sands wind farm and Dungeness nuclear power station.

Friends, I was just chatting with my heat pump (HP – he/him) the other day, when HP made an odd request:

HP: “Michael, would you and Stephanie mind going away for a few days?

I was honestly a bit alarmed. This is our home and although we have taken HP in and hope to provide him with a loving home, we really don’t want him to take over! But then HP explained.

HP: “I’ve got this issue with my Weather Compensation. And when you and Steph are inside the house, switching things on and off, cooking, and just generally heating the place with your fleshy metabolisms, I just can’t see if it’s working or not!”

It still seemed a bit previous, but after discussing it together as a family, Steph and I agreed to go away for a long weekend in Winchelsea and to leave HP to look after the house.

When we came back…

On returning, we were worried we might find the house trashed – you know what youngsters are like.

But in fact the house was pristine and HP had kept the temperature stable all weekend – all by himself!

And to cap it all, HP had left us with a whole pile of beautiful data. I was so proud that I told him I was going to share it on my blog.

Weather Compensation

Looking at 72 hours of data without us messing things up, it was clear that HP really did have good weather compensation.

As the external temperature went down, HP responded by increasing the temperature of the water flowing in the radiators.

The effect of HP’s efforts was to keep the internal temperature within ± 0.3 °C of 20.5 °C over most of this period.

And it is also worth noticing how low the flow temperatures were, peaking at just under 34 °C when the external temperature fell to 7°C.

Click image for a larger version. Graph showing the external temperature (°C) and the flow temperature (°C) of water in the radiators over the 72 hours starting at midnight on 10/11 November 2021. The grey dots show the data every 2 minutes and the green curve shows the data averaged over 1 hour. Notice how when the external temperature falls, the flow temperature rises. This is called ‘Weather Compensation’.

One can see the ‘Weather Compensation’ effect more clearly if one plots the hourly-averaged flow temperature versus the external temperature.

Click image for a larger version. Graph showing the average flow temperature (°C) of water in the radiators versus the external temperature (°C) over the 72 hours starting at midnight on 10/11 November 2021. The blue dashed line shows the nominal ‘Weather compensation’ curve that HP was trying to achieve.

The blue dashed line on the graph above shows the nominal ‘Weather Compensation Curve’ that Vaillant had suggested that HP should aim for – a curve which Vaillant helpfully label with the meaningless number ‘0.7’.

It suggests that even when the outside temperature reaches 0 °C, we should be able to stay cosy with a flow temperature in the radiators of around 40 °C.

In different houses, different compensation curves can be chosen to match the heat pump output to the heat losses from the house.

And over the period of 3 days, HP used just 19.8 kWh of electricity (275 W) but delivered a whopping 83.7 kWh of heat (1.16 kW) – an average coefficient of performance of 4.2.

Conclusion

HP really enjoyed his time at home alone – he seemed so proud that he had mastered the Weather Compensation which can be quite tricky even for clever heat pumps like HP.

It really is great having HP in our family, and Stephanie and I enjoyed our time away too.

I really wish everyone could have a heat pump as considerate as HP.

P.S. In case you haven’t been following, HP is a 5 kW Vaillant Arotherm plus heat pump.

2 Responses to “A weekend away…”

  1. eenjones Says:

    You may be aware of this already, but if not then I’m sure you’d like to read up on coheat testing. This is a way to experimentally measure the heat loss of a building. It’s quite a tricky process to run the test successfully although the concept is simple (heat the house to a high temperature and carefully measure the temperature inside and out and the energy used to keep it warm). But there are loads of things that can make it hard to get helpful data. There’s apaper on this here: https://www.leedsbeckett.ac.uk/-/media/files/research/leeds-sustainability-institute/coheating-method-for-whole-house-heat-loss/lsi_cebe_coheating_test_method_june2013.pdf
    There’s also s similar thing called P-star testing. This involves heating the building for a short period and then turning everything off and monitoring the rate of temperature fall. This is less disruptive to do and arguably this is similar to what you describe your heat pump doing whilst you went away for a few days. There is ongoing research into how data from smart meters and smart thermostats can figure out the thermal performance of a house just by monitoring the data over several months (essentially doing several mini P-star tests) whilst allowing the occupants to control the heating how they wish.

    • protonsforbreakfast Says:

      Hi. Yes, I am aware of similar systems, some of which are now commercial. I think the operation puts thermostatically controlled heaters in every room and records the power used to maintain a stable temperature. If the outside temperature is low, this can give a good indication of the overall heat transfer coefficient and the hearing required in each room: basically an experimental version of the MCS whole house survey.

      At this moment I cannot remember the name of the company offering this.

      All the best

      Michael

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