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Author Topic: One year in... some GSHP numbers  (Read 17091 times)
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« Reply #60 on: December 24, 2017, 12:11:49 PM »

Thanks... thatís very interesting, thatís about 33% duty cycle for both of you.  Of course you do want some headroom to accommodate warming house up from cold, or being able to turn off the heat pump for the evening peak if we ever get demand pricing...
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« Reply #61 on: December 24, 2017, 02:03:51 PM »

Thanks for all the data davec/titan.  What % of the time do these gshp systems run on the very coldest days?  (And do you feel warm enough? - appreciate it is a bit subjective and depends how you have the thermostat set).  Iím asking because I wonder if, in general, the heat pumps themselves are a bit oversized for 24hr operation on the coldest days and in fact you could get away with something smaller. (As long as you have the right approach with leaving it on continuously and not trying to heat up house from cold when you are in it!)

The gshp should be sized for the maximum heating load certainly not oversized. The coldest here so far (2013)  was -12 C for almost a week  and that week it used 130 kWh which at 2.5kW load is around 6.8 hours  per 24 hours  but that was exceptional, last week with a couple of -6 C nights  it  used 60kWh for the week. The  house is always a constant temperature. I don't have the DHW 305 ltr cylinder as part of the normally on system just heat it as required which works fine, the tank is never cold and is up to 55 C in around 20 min, I think it saves unnecessary heating and standing losses but others will probably disagree or have different lifestyles.
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« Reply #62 on: December 26, 2017, 09:31:56 AM »

... being able to turn off the heat pump for the evening peak if we ever get demand pricing...

We never turn the actual HP off but its internal controller does offer 'raise' and 'lower' timers for the compensation curve that we've set so the thing 'prefers' to run in the E10 low-rate times; there's also a standard CH programmer that runs the demand pumps to match occupancy and lifestyle. The rest is left to the exterior temp sensor plus thermal inertia.

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« Reply #63 on: December 26, 2017, 11:57:11 AM »

Good Morning All,

As I've noted elsewhere the heat pump here operates 24/7 and modulates the output dependent on return temperature and the external air temperature.

This holiday period is the first time the four family members have been in the house and us all dependent on the heat pump for domestic hot water (the electric shower having been removed in summer). SWMBO wasn't terribly happy with their not being enough hot water for her bath at the end of the evening on Xmas Eve.

Yesterday evening saw us needing water for the two boys and myself having a shower, SWMBO having a bath and needing water for washing up those things that didn't go in the dishwasher. As the process was started sufficiently early in the evening the system coped (just). It did involve selecting the highest hot water temperature i.e. 58 degrees C to make it work and thus the heat pump/ immersion heater functions were operating every 30 minutes (for 30 minutes at a time) to achieve this.

This is the same situation if we are in the flat in Aberdeen to a degree except there of course the boiler can be 'forced' to focus on heating the hot water only rather than the operator being limited to only 30 minute bursts of water heating.


« Last Edit: December 27, 2017, 07:07:41 AM by linesrg » Logged

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