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Icy cold weather, weather compensation and consumption

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Air Source Heat Pumps (ASHPs)

Last Post by HughF 5 months ago

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Mars

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Topic starter 27/11/2023 10:28 pm

Thought I’d share this as a point of comparison. Two winters ago, our heat pump had been set to run the heating at a 45C set point. When we hit 0C for 24 hours, we did 120kW in electricity consumption. Admittedly, it was a happier time when we were paying 11p per kWh.

This winter it’s all weather compensation for us. Here’s our consumption over 24 hours with temperatures dropping to -2C and rising to 3C. Cold. While the 82 kWh is still high, that’s our full electricity consumption for the day including cooking (and I home brewed which uses power for a few hours). Our ASHP is an 18kW unit.

The house is warm, 21C in most areas.

Feel free to share your consumption data.

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MikeFl

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28/11/2023 9:57 am

This will be my first winter with my HP, and it currently seems to be struggling ... it's been trying for 3 hours to hit the target LWT for 0°C (46.5) but the interference of the defrost cycles keeps pushing it down. 3 days ago we didn't get above zero all day, and couldn't get about 20°C without additional heaters. My estimated COP is hovering just below 2.

Consumption peaked around 45kWh. These temperatures are more like January than November though!

(red line is LWT; orange line is OAT, averaging 0)

Grant Aerona 3 10kW

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iancalderbank

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30/11/2023 6:19 pm

mine for the 29th, max 3C day then -2 at night. 41kwh of electricity for 110kwh of heating. short-term COP is nearly 3 when it stable running in heating mode but the frequent defrosts bring it down 10% ish.

@mikefl if your system is struggling to reach target LWT with the frequent defrosts, that could make it worthwhile looking at your overall system to see if you can run with a lower WT?

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MikeFl

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30/11/2023 7:07 pm

@iancalderbank Yes, that's something I'll be looking at. But I'm trying to hold off changing any WC parameters until I've sorted out the flow rates / balancing / commissioning, etc. (i.e. the stuff the installers should have done before leaving). Right now, I want to be confident the monitoring I've added is stable and accurate, so I can actually see the impact of any changes I make. And my strategy is "change one thing a week and see what happens", which is slow, but hopefully fruitful.

Grant Aerona 3 10kW

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Morgan

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01/12/2023 7:23 am

OUCH! 😲

Yesterday.

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.

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Gary

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01/12/2023 8:04 am

@morgan I beat that by 2kwh

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Morgan

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01/12/2023 8:07 am

Posted by: @gary

↑

@morgan I beat that by 2kwh

-- Attachment is not available --

@gary I somehow doubt you are seeking awards and congratulations. 🤣

Dreading today's readings given the temps overnight here.

Retrofitted 11.2kw Mitsubishi Ecodan to new radiators commissioned November 2021.

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Kenneth

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01/12/2023 4:28 pm

I recently installed a 5kw Mitsubishi ecodan to heat a small barn conversion- ground floor 35m2 with ufh. 1st floor ufh under engineered floor.

I’ve been reducing the flow temp and find that at current temperatures (-1 to -4) that a flow temp of 26c keeps the room comfortable at 20c

A couple of questions

is that flow temp too low for the heat pump to operate properly?
Is the delta t of around 2c too low?

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Gary

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01/12/2023 6:55 pm

@kenneth Ecodans don’t modulate down well I have ufh and it won’t run below 32C without cycling on and off which is what you are seeing. The delta T is low as the flow temp is close to the actual temp of the room so the ufh can’t transfer the heat hence only a 2C difference between flow and return. Delta T isn’t an issue, a lot of cycling is bad for the compressor. You could turn up the flow temp and let it get the room to temperature quicker then let the thermostat turn it off and on as required. You would get less cycling and shorter run times the energy consumption msg not be much different

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Kenneth

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01/12/2023 10:01 pm

@gary Thanks for the advice. I will increase the flow temp and see what happens. If it gets noisy at higher temps I might revert back - neighbours haven’t complained about the noise but when it’s working hard it seems quite loud. From my point of view I’m relieved it’s working well heating this house. Lots of insulation in the floor ,walls. And roof have paid off. Minus 4.5 now outside but still 21c in here.😊
kenneth

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SUNandAIR

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02/12/2023 8:37 am

30th November was a bit cold we operated a setback to 16C and still got a TOPUP in the middle of the night

Room temp is black line. Green is Outside temp.

Flow temps for us typically around 40c with an all radiator system.

17th C house, 180sqM area, 21kw Rads (DT50), 8.5Kwh Ecodan, operating in Auto Adapt

typical defrost and recovery back to 40C

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Dunlorn

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02/12/2023 8:49 am

-10°C here overnight and still currently. House is just about at 18°C, so comfortable, but we've pulled 41kWh so far today. 😱

The one noteworthy thing, apart from eye-watering consumption, is that defrost frequency has been only around every 80-90 mins which has allowed the LWT to reach set point. Presumably this is a function of humidity - at around 0°-2°C with damp air or snow falling the defrost frequency can be every 30-40 mins so the LWT never really builds to its target.

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