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Heat pump delta T too low - 2c

Benseb · 2022-11-09T12:30:05Z

So we have an Ecodan 14kW heat pump. Had it a few years and it’s worked well but a bit expensive. whenevrr I’ve checked the stats the delta between flow and return has always been 5c on the dot. This year I’ve been balancing radiators and removing zones to make one big zone to improve efficiency. Which it has! However I’ve noticed that now the Delta T is 2c most of the time. 3c max. Which would indicate not enough heat is leaving the rads / UFH? What do I need to check/adjust?

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Air Source Heat Pumps (ASHPs)

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Derek M

(@derek-m)

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Posts: 4425

24/01/2023 12:12 pm

Posted by: @scrchngwsl

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Posted by: @william1066

↑

@scrchngwsl

in theory, the emitters won't be emitting any more heat, and the heat pump won't be using any more power.

The above is not entirely correct, since an increase in LWT will actually cause the heat emitters to 'emit' more heat energy.

Consider the following:-

If the outside air temperature is 10C, with the indoor air temperature at 20C, a fixed LWT of 35C and a water flow rate of 15 litres per minute.

The outside air temperature falls to 5C, which increases the heat loss of the building, since the DeltaT between inside and outside is now 15C. The inner fabric of the building starts to cool, which in turn has a cooling effect upon the air within the rooms. As the cooler air circulates around the rooms it comes into contact with the heat emitters, and creates an increased DeltaT between the room air and the outer surface of the heat emitters, and hence has a cooling effect. The fall in temperature at the outer surface of the heat emitters is reflected at the inner surface, which in turn has a cooling effect upon the water flowing through the heat emitters.

Because the LWT and the water flow rate are in this case being held constant, the heat energy produced by the heat pump will initially still be the same. The heat emitters, on the other hand, are absorbing more heat energy from the water, which has the net effect of causing the RWT to reduce slightly. This slight reduction in RWT will increase the DeltaT between LWT and RWT, causing the heat energy output of the heat pump to increase slightly.

Without any further changes in operating parameters, the system should achieve equilibrium with a reduced indoor temperature of say 19C or even 18C.

To keep the indoor temperature more constant during the above scenario, most heat pump controllers sense the increase in DeltaT between LWT and RWT, and have the capability to increase the water flow rate by increasing the water pump speed. Although the LWT remains constant, the increase in water flow rate transfers more heat energy from the heat pump to the heat emitters, thereby supplying the additional heat loss of the building.

If the heat pump is operating in WC mode during the above scenario, the falling outside air temperature would automatically cause an increase in the required LWT produced by the heat pump. Any change to the specified DeltaT between LWT and RWT being corrected by varying the water pump speed.

A correctly optimised heat pump controller should therefore be capable of keeping indoor temperatures reasonably constant under normal operating conditions.

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william1066

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24/01/2023 12:49 pm

@derek-m Exactly, I had this formula for UFH, though not sure it is correct but seems to give results in a reasonable ball park. In any case the results illustrate your point.

G7 is room and H7 floor temp

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iancalderbank

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30/01/2023 11:37 am

@william1066 I think the bellimo valves that @heacol recommends are back in stock at JTM, I'm tempted to grab one for my build before he gets them all again 😉

My octopus signup link https://share.octopus.energy/ebony-deer-230
210m2 house, Samsung 16kw Gen6 ASHP Self installed: Single circulation loop , PWM modulating pump.
My public ASHP stats: https://heatpumpmonitor.org/system/view?id=45
11.9kWp of PV
41kWh of Battery storage (3x Powerwall 2)
2x BEVs

👍

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Brendon Uys

(@heacol)

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30/01/2023 12:31 pm

@iancalderbank 🤣 🤣 🤣 we are going to be stocking a better one.

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iancalderbank

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30/01/2023 1:07 pm

@heacol so if I'm going to replumb in a couple of weeks will you be selling by that point, or just get a bellimo from JTM?

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Brendon Uys

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30/01/2023 6:29 pm

@iancalderbank should be. Our stock should arrive week after next.

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iancalderbank

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06/02/2023 11:25 am

Posted by: @william1066

↑

That is my current choice for replacement of existing one. At 45 lpm is 1 mh2o.

-- Attachment is not available --

INTATEC.CO.UK "https://www.intatec.co.uk/wp-content/uploads/2022/03/Technical-Datasheet-IKHPMF28-Intaklean-Heat-Pump-Filter-r6.pdf"

@william1066

doing some component research over the weekend. spirotech 1 1/4 "

https://www.spirotech.co.uk/products/spirotrap/spirotrap-mb3mbl--brass--magnet--uni-118/?variant=948

pressure loss spec took some hunting down but its 2.2kpa (0.22 mh2o) at 3.6m3/h, which is way better than the typical 28mm ones that are sold.

https://spirotechdirect.co.uk/files//592434c9-322d-405a-bb4c-a88a00b069ca/Leaflet%20SpiroTrap%20MBL_F_NR-2130.PDF

pricings not too bad, available in the usual places. There's even a 1 1/2" one if you wanted even more headroom.

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william1066

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06/02/2023 9:41 pm

@iancalderbank You need the chart, because given a big enough pump you can probably get a pretty high flow rate. I would ideally like less than .5 mh20 lost through a filter.

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william1066

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06/02/2023 9:43 pm

Posted by: @iancalderbank

↑

pressure loss spec took some hunting down but its 2.2kpa (0.22 mh2o) at 3.6m3/h, which is way better than the typical 28mm ones that are sold.

This is definitely acceptable, do you have a link to the pressure loss chart?

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iancalderbank

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07/02/2023 10:27 am

@william1066 3.6m3/h with a DP of 0.22mh20 means its not relying on a monster pump. the chart is here

HASL.CO.UK "https://www.hasl.co.uk/wp-content/uploads/2013/11/SpiroTrap_Eng-HASL_14461_03.pdf"

I was comparing to some of the usual suspect 28mm versions on offer (including the spirotech one) its a substantial difference.

there's also a a caleffi one https://buyplumbingonline.co.uk/altecnic-dirtmag-brass-dirt-separator-1-1-4-546307-caleffi.html

DP is better again, down to 0.5kpa = 50mm h20 , at 60l/m for the 1 1/4"

spec sheet

https://www.altecnic.co.uk/wp/wp-content/uploads/downloads/5468%20Dirtmag%20Vertical%20Bronze%20Data%20Sheet.pdf

I'm about to order one.

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william1066

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08/02/2023 11:59 am

@iancalderbank Thanks for that. I quite like the ESBE diverters, but can't seem to get the one I need here in UK. Also trying to connect 28mm to 1 1/4 will be a pain. I am not a plumber by trade, just a diy plumber, and like the simpler options 😀

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iancalderbank

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08/02/2023 12:09 pm

@william1066 I'm exactly same as you. keen DIYer' . I'd prefer it if the filters came with 28mm connections, but those are all too small bore inside. I don't want to go with just a strainer. 28 comp to 1 1/4" is simple. https://www.monsterplumb.co.uk/compression-male-straight-coupling-28mm-x-1-1-4

diverter there is the the bellimo R3025-S2-LR230A that @heacol recommends (unless he gets his new ones imminently) I'm intending to do that part of the plumbing v soon. anything particular for the ESBE versus that one?