Rather then setting a max output relative to heatlose there should be a minimal output the heatpump can modulate down too relative to the heatlose.
Shame it not practically to give installers a boses based on heatpump electricity useage compared to past gas usage.
That the classic case for adding fans to the smaller radators.
Or just take the new Cosy 9, with a little lower claimed COP then Diakin 9kw but will modulate a lot lower.
Are members of this forum more likely to have reasonble airtightless then the public? Eg can we use our data to predict how much over estimated normal peopleās heatlose is?
As electricity costs the grid a lot more on very cold days then on days we need a little heating and electricity tariffs are moving closer to matching real costs, should we be optimising to maximise COP or minimises cost of generation? Likewise capital spending on electricity distribution system tends to be driven by the days with highest demand, but at least in the short term charged to us based on our total yearly electricity usage.
the housing stock might be better than the uk goverment and media paint the picture
so the results after our legal requirements are not met makes it look like we have made great strides
I think if the grants premitted, with what I expect my calculated heatlose to be, I would want a undersized A2W combined with a very basic A2A as addational capacity in living room. (Over half our floorarea can easily get some heat from livingroom if the livingroom is at a little higher temperature.)
We have the issue that at present we heat to significantly lower temperature then the British Standard for heating design requires but when we are in our 80s are likely to want at least the standard temperatures. So if we could size a heatpump based on gas usage, I would size pipework and electric connection based on British Standard so easy to swap to larger heatpump.
But with the rules as they are, I can move all the addational electricity usage due to low minimal output to cheaprate with Ā£3k of DIY Fogstar batteries, but will need to buy significant daytime electricity for the coldest 2 or 3 weeks of the year regardless of what I do with batteries. Hence I care most about COP for these coldest weeks.
So should a 4 port buffer with mixer in CH side be used for the rast of the year to give high comfort with a few values that converts it into volumizer (or removes it from system) for coldest weeks?
So a UFH manifold with mixer/pump, and a presure sensitive bypass on a volumizer. Run manifold mixer with weather compensation when heat demand is low, with Daikin keeping ābufferā between 30c-40c. In peak heating season, close bypass and set mixer on max (ideally have value to bypass manifold pump) using heatpump weather compensation. (But donāt need to install such a setup unless oversized Daikin proves to give unstable floor temperatures at required flow temperature.)
There are some wider studies on this, that indicate average air change rates in the 0.5 ACH range, but there is also often quite a spread of values. Iād like to understand a bit more about how difficult it is to reduce the air change rate on a property that is quite leaky e.g starting around 1.0 ACH, bringing it down to 0.6ACH. Is the higher end properties with older sash windows and doors both with sizable unsealed gaps and open chimneys perhaps?
I have made no effort at all to improve the air-tightness of my own mid-terrace solid stone house which has standard double glazing and doors. Both a blower door test and the CO2 monitoring suggests itās typically 0.6 ACHĀ±0.2. (Though it can push up to 1.2 ACH or so when we have a very strong wind storm blowing at the front elevation). Which makes me wonder what the impact of basic drought proofing could be on leakier houses? I do think this house could benefit from more drought proofing but it would need to be combined with better controlled ventilation.
It has a massive effect. If you look at the studies of the Q-Bot the airtightness effect particularly on timber suspended ground floors was quite staggering.
It can also be very significant what type (if any) floor covering is layed over the suspended ground timber floor. Floor coverings get changed by new residents but heatpump design need to work for all likely residents of a home over next 30 years. (Unlikely primary pipework will be changed even when heatpumps are replaced after 15 years.)
Iāve been using my gas usage to get an idea of heat loss. Donāt know if its an accurate method to use. Iāve enjoyed it. Kids and wife think Iām mad.
House is 6 bed.
306mĀ²
9" solid brick walls.
New roof and windows in 2014.
I have 9.24kwp solar
10 kwh solaredge battery
6kw solaredge Homehub inverter. Dno 6kw.
System produces around 8Mwh. I exported 2Mwh last year.
Iām insulating the 116mĀ² crawl space at the moment. Using ybs superquilt.
Boiler is a Worcester 40kw cdi. 17 years old.
I have a wood stove.
The last 4 years gas has been around 34000kwh. Ā£2,000 on gas.
The bill for Dec, Jan was Ā£415. Gas used 6221kwh. Heating was on 24/7. Internal thermostat was set to 20.5c. This is the worst case scenario.
I set the radiator max temp to 50c and surprisingly the house was comfortable even on the colder days. - 5 and the house was 19c. Yes, boiler on all the time at theses temps, but the house was comfortable. The internal thermostat only started to climb when outside temp got to 0c.
In jan/dec 2021 I used 6800kwh of gas. That was another cold month and the boiler was set to the on and off method to heat the house. House set to 19.5c
Soā¦Last week ive reduced my boilers maximum output to 13.4kwh and Iām using 10.2kwh of gas to heat the house. . My rad max temp is 49-50c.
25th Jan used 167.73 kwh of gas. House was set to 20c. Outside temp was 0c overnight.
(Just a small nit pick: you mean kW here if youāre talking about instantaneous power.)
Factoring boiler efficiency, the actual heating power is somewhere between 8 and 9 kW at 0Ā°C. Extrapolates to around 10 kW at a design temperature of -3Ā°C.
The 12 kW model seems a little oversized, but not unreasonably so given the size of the property. Having a big extra will help cope with defrosts.
What did the heat loss survey say?
Your property sounds similar to this one which HeatGeek and SkillBuilder did a detailed re-install. Checkout the two videos listed.
interesting @Alan_Bennett putting your house into Simple heat loss tool i get 15.5 kW assuming 0.6 ACH, -1.4C outside design temp and 23.8 kW assuming cibse defaults, what did the heat geek heat loss calc say?
Your gas day suggests 7 kW average on that day so quite a gap thereā¦
I also calculated the 7kW average for 25th Jan, but then realised that it was only 0Ā°C overnight and warmer during the day, so figured it wasnāt representative of a cold day. It would be helpful to see daily gas consumption for the period around January 8-11th.
Ooo nice! Your gas readings clearly dont align with this but they also dont align with low air change rate assumptions in the heat loss calc and so Iād want to get a better handle of why that is.
6200 kWh Dec/Jan = ~16500 kWh/year, half the 34,000kwh/year you mentioned above?
34,000 kWh/year gas = 28900 kWh heat which is close to 12 kW.
Maybe the contribution from the wood stove could explain the difference to my 15.5 kW at leastā¦
I burn around 6 tonne bags of wood per season. 8kw stove. The lounge has 3 outside walls and is a big room. Lounge temp is fine if the heating is on (all internal doors open throughout the house) . The lounge does cool down quicker than other rooms. Itās the main reason why Iām insulating the crawl space to improve the lounge. ( I hope) Lounge is around 41mĀ²
On the 8th jan the temp range was 3c to -5c. 6hours was at - 5c. House temp was 19c at 8am with outside temp of -1. House temp didnāt increase until outside temp got above 0c
Boiler flow rate was reduced to 50c max on rads. Boiler was still set to 40kw.
I would have the stove on but just ticking over.
Leaving the heating on 24/7 I havenāt needed the stove on as much.
Lounge is 20c at mo. House thermostat is saying 20c. The other two thermometer in the lounge are saying 19.8c and 20.2c
Outside is 4.8c
Rads in lounge are 46c. Iām only using cheap equipment to measure temps. I take the numbers with a pinch of salt
Thatās more like it, so 11.8 kW gas, maybe 10.6 kW heat.
Aligns roughly with your 34,000 kWh heat/year
6 ton bags is not 6 tons itās more like 6x 350kg i think x 3000 kWh/kg = 6300 kWhā¦ x 70% efficient stove = 4410 kWh heat. This gets us closer to the lower end heat loss I calculated of around 15.5 kW!
itās more like 6x 350kg i think x 3000 kWh/kg = 6300 kWhā¦ x 70% efficient stove = 4410 kWh heat. This gets us closer to the lower end heat loss I calculated of around 15.5 kW!
