waxingsatirical

Just to be clear, 15.5kWH is the energy drawn by the heat pump not the heat loss for the house. But yes, it does seem low, the house is not especially well insulated, it's a mix of filled cavity/unfilled cavity, pretty-well draughtproofed though and loft-insulation is good. It's a semi and a cube, so that helps, and only 1500sqft. I'm now thinking that the heat-pump is under-estimating the energy it's generating. I don't know how it's working it out. I guess the difference between flow and return temp multiplied by the flow rate. Would explain the low heat-loss and the poor COP. I put the hot water on the immersion for a few days, to take that out of the equation, and it didn't make much of a difference to the COP, still only just above 3. Also, my COP figures are "energy-weighted", meaning I take a day's worth of energy out and divide it by a days worth of energy in. So this would give a lower COP than "time-weighted", where you would take multiple readings of the COP throughout a day and average them.

For anyone following this, thought I'd give some updates. House has now been running on ASHP for about a month. There is no problem heating the house, haven't changed any rads but still mainly runs between 30 and 40 degrees. For second half Nov/ first half of December it's used on average 15.5kWH per day, which includes hot water, COP (according to the device itself) is about 3.25, but again this is including hot water. The heat loss matches pretty well to my measured heat loss from last winter, but the heat loss calculation was over by a significant amount. As for the installer, still have some issues to resolve with them, might give a detailed update once everything settled. Still haven't paid. Won't be recommending the local company. Octopus would have probably been a better choice.

Thank you all for your input. Presumably then, my system will be doing some kind of load compensation based on the return flow temp. If I set the thermostatic valves on the radiators, then as they turn off return temp will increase more quickly and the ASHP will be more responsive? Or is this a bad idea?

Please tell me I am wrong with my understanding of weather compensation. A compensation curve is setup which relates the outside temperature to the target flow temperature. Cold outside, high flow temp. Warm outside, low flow temp. So the internal temperature is not taken into account? If so, what happens when I light my 4kW wood burner? Does the heating system just merrily keep inputting as much heat as it assumes the house needs?

Good shout. I just did the online Octopus quote, which takes literally 20 seconds. It came out a few grand cheaper, but once they've done the survey I'm sure would go up a bit.

Thanks for your input, I value actual experience over predictions from models. I measured my home's heat loss last winter, in a cold snap, and it came out to 3.5kW, well below the calculated value. See the inflammatory chain started by me last spring. I figure I'll be able to run lower than 50.

Ha ha, no it's loads! But it's hard to even find someone to do the work, I've been chasing these guys for the last year to try and get an install date. Besides, I thought the point of the grant was to bring the cost down to an amount comparable to that of getting a new gas boiler? Not to hand out free heating systems.

Yes the calcs use 50C out 45C return, single zone. The buffer tank is integrated into the heat pump apparently, can't see how you'd fit much of a tank in there or why having it outside is a good idea.

Thank you, I will query this with them Looks like they have used 50C out 45C return. I'm getting an electric car, which I'm sure will mop up any unused electricity. I am asking them to fit a charge point at the same time.

The radiators are already oversized, there may be some that need to be swapped out for larger ones, but I have agreed to do this at a later date if needed

For anyone who was following this thread some months ago. A few weeks ago my old cold water tank sprung a leak, not from a joint, the tank itself. No, I hadn't been playing around with it, it hadn't been touched in the 20 odd years I expect it sat there. I saw the drips coming through the ceiling as I read my son a story before bed, he would have gotten very wet, or worse, if I hadn't spotted it when I did. This confirms my dismay at the lack of leak proofing being fitted loft tanks, and strengthens my resolve not to repeat the error when I have the (now new) tank replaced.

Hi All, I'm on the verge of accepting a quote for install of ASHP into my property, would any of you mind giving me your opinions on the setup? I'll just try and give you the key information, as obviously there is a lot of detail, but please ask if I've left anything important out. This is for a 4 bed property, 1500sq ft, traditional radiators, well insulated, mostly filled cavity, some unfilled cavity. Building Max Heat Loss: 5.6kW Daily Hot Water Demand: 45L Hot Water Temperature: 50C Legionella Purge Temp: 60C Legionella Purge Freq: Weekly Samsung Mono R290 - integrated pump and expansion vessel Cylinder "sized to heat input requirements" Solar PV 7 panels (this is all there is space for) Thanks in advance

I guess some sort of bunding tray, with a leak detector to shut off the mains would offer some protection. Not the off-the-shelf system I was hoping for though. Probably not going to bother. Thanks for your answers though.

I didn't install it

Hi, I'm having my heating system overhauled and as part of that a new pressurised hot water tank is being installed in the loft. It's going to be a lot of water above the house, so I am worried about what would happen if there were a leak. I asked the installers what they can provide in the way of leak protection and they have said that there isn't really anything on the market, people don't generally do it. In my mind I have this picture of a the tank, and all joins in the pipework sitting above a set of trays, each draining to an overflow that goes out the exterior wall. Does this sort of system not exist? Is it not feasible? Is it just not worth it?

Well, I wouldn't say "uninsulated". It's a semi, so one side is warm anyway, the other side is 00s extension so filled cavity, the front and back are a mix of original unfilled cavity and extension, let's say 50/50 for simplicity. The loft is up to spec... nearly. The doors and windows all seal well. I've installed mechanically closing extractor fans as well.

Yes, calorific value is ~40 according to my bill and my factor includes a metric conversion factor of 2.83

Thanks for these, his 'coldest day' approach is basically the same as my approach which has given me more confidence in my figures.

Wow, I'm impressed by the depth of this discussion. One thing that I clearly need to do is take account of the efficiency of my boiler, it's condensing but must be at least 15 years old, and yes comes on and off throughout the day as it's needed. 85% seem reasonable?

...when you can measure? OK, I'm talking about retrofitting, obviously, you can't measure on a building that is yet to be built. I have just had a conversation with a heating engineer about conversion from gas boiler to heat pump, who was not interested in any of my gas usage over the past few cold months. Instead, he would only rely on a heat loss calculation. I did a heat loss on my property a while ago, and it came in at 3.3kW @ delta T of 20. Which seemed a bit low, also I wasn't sure about a few things, like accounting for loss through the floors. I decided to measure my gas usage over a cold snap back in Jan, which came out at 3kW, outside it was -5 at night, just above freezing in the day, 19 on the thermostat. Again, seems a bit low for my property. My house is a 1950s built 4 bed, 1500sq ft semi, but large 2-storey extension so not a lot of the old unfilled cavity wall exposed, new double glazing last year. 1. Is there something wrong with my reasoning, isn't usage the best measure of heat loss? 2. Maybe someone could check my usage calcs, as they seem low to me 9 units * 31.9 conversion factor from my gas bill ~ 300kWh 4 days ~100h = 3kW

I have a 1500sq ft semi in Buckinghamshire, built in the 50s but large wrap around 2-storey extension in 2000s. Currently running a gas boiler. I've been putting a lot of effort into draughtproofing and insulating, to cut heating costs. Now looking at options for heat pump with a view to getting off gas.