ReedRichards

What you have achieved is excellent and I'm sure it's best to play safe and have long cycles rather than short ones if you can. But in the same way that some concepts that apply to internal combustion engine cars don't apply to electric vehicles (such as optimum mileage per unit of fuel at around 56 mph) I wonder if short cycling really is bad for heat pumps?

References? I sometimes wonder if short cycling, which is a valid concern for fuel-burning boilers, has been carried over as a concern to heat pumps without justification. I doubt that anyone worries about short cycling with an electric boiler so what goes wrong if a heat pump?

Do you have one? I think the previous sentence misses a "not" so the meaning is inverted. Should say: I have both a Therma V and a DHW recirculation pump and they function perfectly well completely independently.

How warm is it inside the house?

If you are using pure Weather Compensation then the ASHP will be on when the scheduler is on but the room temperature has not reached the temperature set on the thermostat. "On" might include cycling under some circumstances, such as mild weather. This happens when the ASHP cannot operate at a low enough power output to remain on continuously.

This device lets you monitor the energy used by any appliance and can also be used as an on/off timer https://www.amazon.co.uk/dp/B0B831STBX?ref=ppx_yo2ov_dt_b_product_details&th=1 (the pack of 2 is currently priced as only £1 more than the single).

Even so, can you not ensure that the insulation standard is good enough that you don't double the heating requirement of the house?

I do but I don't. I heat up my DHW cylinder with off peak electricity using my heat pump.

Do you have any of: Swimming pool? Hot tub? Electric Aga? I would have thought that just using an immersion heater you would be hard-pressed to use 150 kWh per week heating your hot water. If you were heating water from 10 C to 60 C using an immersion heater you would be using over 2500 l of hot water per week to consume 150 kWh. That's possible but your household would need to be taking several baths per day, in which case you would have had a big fuel bill in your previous property however it was heated.

More context, I live in a timber frame bungalow built in 1980, about 195 m2, (based on the external dimensions). My heat pump used about 6500 kWh last year for heating and hot water. It's never turned off so the heating will come on on a cold day in summer, but I use Weather Compensation so it does not have to work very hard then.

I'm tempted just to offer this:

The field mice that like to overwinter in my loft love to chew on pipe insulation but don't seem to like the stuff with an aluminium surround. So aluminium foil may be a good idea if there is any chance of rodents getting inside the duct.

Don't forget you also need a second had oil tank and the pipe connecting one to the other. And when you do replace the oil boiler make sure it is when you run out of oil so that's not wasted. And if you are thinking of getting a heat pump eventually make sure all your internal plumbing and components (radiators if used, hot water cylinder) will be compatible with a heat pump at the maximum water temperature you will choose to use. This will almost certainly cause your oil boiler to cycle quite a lot.

But both feeds are from the one heat pump so having one zone for the UFH and a second zone for the radiators doesn't really help. Maybe at the moment perhaps your ASHP is set to produce water at 30 C to meet the requirement of your UFH whilst it's mild out, but that means your radiators are fed tepid water at 30 C. Or if you turned off Weather Compensation you could ask your heat pump to produce water at 50 C. That would keep your towel rails nice and warm and the manifold on your UFH would use the return water to dilute the input down to the 30 C it needs but now you are running your heat pump much less efficiently.

I have all radiators and the bathrooms have towel rails. A problem I find is with Weather Compensation; unless it's quite cold out the towel rails only get tepid so the towels don't dry out very quickly. I would have thought that running UFH and a towel rail would make that even worse because the UFH would need an even lower output temperature from the ASHP. Who wants tepid towels instead of nice warm ones?

My feeling is that in the real world DHW cylinders lose a lot of heat by conduction down the connected pipes and this isn't taken into account in tests.

My understanding is this. Hot water cylinders are well-insulated so even an inefficient coil will get your tank to temperature eventually but it will take longer and whilst the heat pump is heating the hot water it isn't heating the house. So when it's coldest outside the time spent heating hot water might be too long to keep your house/flat warm enough. Presumably you could get around the issue by up-rating your heat pump output so it can keep your building adequately warm with only 22 hours worth of heat per 24 hours, or something like that.

In summer you won't be using the ASHP much so it's likely you'll have lots of spare electricity to export so you need a good export rate. In winter the ASHP will gobble up any solar power you generate, probably without making much of a dent on what you import. So you need a tariff that gives you a low import price for most or all of the day because an ASHP typically runs for long hours. Good luck with that, cheap imports and a good price for your exports, the two rarely go together.

It was in 2020 that I was looking at this. After wracking my brains for a bit I remembered that it's ESBE who do the most integrated unit and you can now buy one on eBay for a much more reasonable price than I could find then. Here are some details: https://esbe.eu/group/products/thermostatic-units/vtr300-vtr500 . Oh, here's a nice little video:

There is a rather complicated plumbing arrangement you can use to fix this (see figure 4 https://www.hpacmag.com/features/recirculating-domestic-hot-water-system/ . In the North America you can buy this as a single integrated unit but they're not available here for any reasonable price.

I thought the correct way to plumb the TMV was to run a loop of pipe down from the top of the cylinder then position the TMV at the bottom. Hot water from the cylinder can rise up to the top of the loop but for heat to travel down to the TMV it has to work against convection so the TMV stays suitably cool and lives longer. I cannot remember the exact length of pipe you can use for the loop but you should be able to look it up.

If your AI mode is anything other than zero (and this is not just a temporary adjustment) it means that your Weather Compensation temperature settings are slightly wrong. In your case the Leaving Water Temperature must be set 2 degrees too high so you should reduce your WC temperature settings for the LWT by 2 degrees then set AI=0. It's not critical to do this but it restores the full range of adjustments you can make, down or up. However I'm really glad you have the comfortable warmth you were seeking. I've never found any indication that the LG controller can program the AI setting, which is the only way to do a night-time setback unless you use Air + Water on the controller and can program a target temperature for the room the controller resides in (I can't remember the details of your set-up). I don't think there is an easier way. If the LG Therma V heat pump does record any heat output data, this is not made available via the controller. That's a bit terrible. I can't believe even the least competent plumber would make a mistake like that.

So maybe if you don't live in an airtight house (and sadly I don't) then you can't do the type of thermostat-free Weather Compensation that you favour? At least not in the depths of winter when opening an exterior door can reduce the temperature of the room it leads into?

I disagree. There are different ways you can do Weather Compensation. The most radical way is to try to balance the heat loss from the house with the input from the heat pump. So you don't do anything internally that could cause this heat loss to vary. You don't use a room thermostat or radiator thermostats. You probably don't leave the house either as opening an external door would lose you a chunk of heat that this regime does not allow for. In principle this is the most energy efficient way you can run a heat pump but is has disadvantages if you don't want the same temperature in each room all the time because "a room takes ages to change temp". You'll find plenty of true believers here who seem to think this is the only way you can do Weather Compensation - but it isn't! Another less radical way to do Weather Compensation is to cut yourself a bit of slack, make the leaving water temperature a bit higher than it would be in the purist scheme but still varied according to the external temperature. This will cause your heat pump to cycle a bit more but get it right and these will be long rather than short cycles. In principle your heat pump will perform a bit less efficiently but it will be able to warm up a room faster if necessary. Now you can use room and radiator thermostats. So you'll probably pay a bit more for your running cost but what this money buys you is more flexibility. This is what I do and it works fine for me.

Do you actually want the night time set-back? Some heat pump zealot is bound to come along and tell you to forget about the room thermostats, that you should be relying on Weather Compensation together with carefully balanced radiators to maintain a constant room temperature. Me myself, I much prefer a night-time setback and, should you want to abandon your room thermostat, that's only possible if your heat pump controller has a mode which allows it.