waxingsatirical

Seems a bit low, I think I'm spending about £5 a day on heating at the moment

Thanks for your input guys. I've been busy with my CO2 monitor to try and figure out how many additional air changes I need in a night to keep the CO2 constant. Then I'm trying to figure out how much heating that air will cost me, to try and decide if it's worth going for mechanical ventilation with heat recovery or not. Here are my back of envelope calculations. Measured CO2 increase per hour at night: 30ppm CO2 output from a sleeping family per hour 30L (From this website https://docs.openenergymonitor.org/heatpumps/measuring_ach_with_co2.html) 100sqm of floor area (rest of house is closed off) x 2.2m ceiling height = 220 m3 = 220,000L Therefore, with zero air changes would expect 220,000 * 30 /1,000,0000 = 136 ppm increase per hour (this is using the 30L family CO2 output) Let's say that indoor is 800 and outdoor is 400, so 1 ACH results in decrease of 400ppm I'm seeing a difference of ~100ppm between measured and calculated increase per hour, so getting 0.25 ACH To acheive a steady state, need an additional ~0.1ACH For 1 cold night: 0.1 * 220m3 * 1.2kg/m3 (air density) * 1005 (heat capacity in Joules) * 20 (temp difference on cold night) * 8 (hours in night) / 3,600,000 (convert to kWh) = 1.2kWh 1.2 /3 (COP of heat pump) = 0.4kWh So what's that? about 5p on the night rate?

Another year another update. Bought a CO2 monitor, as I was hoping to use it to justify closing trickle vents for the really cold months. Turns out that even with all trickle vents open CO2 gets up to ~1300 (forget the units, sorry) at night. It varies a lot with the wind I think. There is a draught coming from the spare room, which I was planning on closing up but instead I make sure I have the door to this room open at night now, which keeps C02 below 1000. This is with a family of 4 in a modest 4-bed house. It does make me wonder why I bothered with all that insulating, and draught proofing when I practically need to leave a window open 24/7. So now looking into mechanical ventilation with heat recovery.... any shared experiences with this would be welcome

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