Forum menu
this is the WC curve for my veissmann gas boiler in a (very) well insulated house with concrete floor and UFH. It should vary the temp by quite a bit.
Ours was installed last summer so this is the first real period of extended cold weather. North west based and temps here over the last week or so have got as low as -5 overnight and daytime temps have been only up to around +2.
4 bed detached and thermostat set at 18c. Our old boiler was set at 16c during the day and up to 19c evening before going to around 12c overnight before back to 16c etc. Both of us were working from home so from this you can gather that we dont like the house too warm. The ASHP isn't as responsive ad the boiler however we allow the temp to drop from 18c to a max of 16c between 10pm and 4am. Then it slowly gets to 18c and so on.
Interestingly (in a good way) despite allowing the system to drop a max of 2c from 10pm to 4am, even in this extremely cold weather (for us) it is only dropping around 1.2c. When we had the system installed the heat loss calcs indicated that we would benefit from improved loft insulation (it is fully insulated but they suggested replacing with 100mm PIR) at circa £1600. I opted to wait until we had experienced a first winter before doing that and so far it appears to me to be an unnecessary expense.
The flow temperature should be 40 degrees maximum, but preferably 35 degrees. Make sure they do a proper heat loss survey, so that the radiators are sized correctly.
This is the by far the most critical factor for air source. I’ve had air source 10 years on a self build and sizing and insulation is everything. The reason is the energy to raise the flow temperature by 1c is not linear as you raise the temperature for air source. This is when it gets really expensive if radiator is are under sized as they can’t radiate the heat energy quickly enough to heat the room so need a high flow temperature. I’m running at 35c and it’s -5 outside.
Hot water I have set at 50c but I’ve got an EV tariff so run extra hot water to 65 overnight via the heating element on cheap 5p tariff.
We have been running one for a year now, it works great house very cosy and never once ran out of hot water, there’s 5 of us. It’s very quiet, the last week or so it’s been -5 to -6 at nights house is sitting at 20 deg. We have UFH on both floors. Monthly electric DD is £130 per month. Will when funds allow add solar and battery.
Tony, run the heat pump on the cheap tariff, more efficient than an immersion heater. Also pre-heat the house if possible or a large buffer during those periods.
Yes the lower you get the flow temp the better, but don't be afraid of 50 deg flow, especially with modern R290 machines, they are capable of 70 deg.
More important is to get the emitters and pipes sized to the correct DeltaT.
I run mine with a max flow of 50, and as I have mentioned on other thread we are saving money compared to running a gas boiler. Some of that is down to other changes we have made, but I live in an old flat, my COP is running at 4.6 for the current week (heating and hot water), with temperatures down to -2 overnight and only just creeping to about 3 or 4 during the day this last week.
Design is critical, how you use them equally so.
Interesting about flow temperatures. I generally run out gas CH at about 45degrees anyway (on our solid walled Georgian semi) but have turned it up to 60 during the current near zero cos snap. .maybe I should have just run the heating constantly?
Back to heat pumps, how are the hot water requirements met? We currently have agas combi, so no hot water tank. Given we're a family of 5 for whom it wouldn't be unusual to have 3 showers and 2 Baths on the same day, and one of the baths is a massive near 300litre capacity, I'm not sure I have the. Space or load bearing capacity on the remaining loft (after a conversion). So what is the solution if there's no room for a hot water tank? And how long to reheat from cold?
Tony, run the heat pump on the cheap tariff, more efficient than an immersion heater. Also pre-heat the house if possible or a large buffer during those periods.
That isn’t how my ASHP system works. For hot water it will use immersion once the heat pump has reached a programmed point so immersion boosts to the requested extra hot water setting. Heating is always on and keeps the house at a set temperature so no concept of preheat. The system will draw on the heat pump to maintain the flow temperature at a level to maintain the house at the set temperature.