help with heat calcs

[Mike_scotland]

hello,

I got this from my builder the other day he got it from vaillant who are the likely ASHP company he is going to use, it may aswlel be chinese to me, just wondering if it looks good? or bad or what really? 

house is around 220m2 with triple glazing but quite alot of windows downstairs and up.

Thanks,

 

[SteamyTea]

Roughly 100 kWh/m².year.

Or assuming 5 months heating, 25W.m² power needed.

 

Do you have any other heat loss calculations?

[Mike_scotland]

1 minute ago, SteamyTea said:

Roughly 100 kWh/m².year.

Or assuming 5 months heating, 25W.m² power needed.

 

Do you have any other heat loss calculations?

so what does the peak heat loss at 7.9kw mean? 

[Mike_scotland]

im also assuming the 24552 kWh/year isnt taking into consideration the co officient? so if i got like 2.7/1 or so it would be alot lower?

[SteamyTea]

Just now, Mike_scotland said:

so what does the peak heat loss at 7.9kw mean? 

That is to cover the 99th percentile. Almost any heating system will be designed to supply enough power, 99% of the time. That 1% us for extreme weather events i.e. -18⁰C or something.

Most of the time a 6 kW unit would do your heatload quite happily. There is a bit added, 2 kW, for heating the hot water.

So seems to be about the right size.

[ProDave]

6 minutes ago, Mike_scotland said:

so what does the peak heat loss at 7.9kw mean? 

That means your heat source must be capable of delivering 7.9kW of heat into the house 24/7 on the coldest day.  Assuming you don't want the heating on 24/7 and allowing for DHW heating as well, you will probably be needing a 15kW ASHP at least.  What have they specified?  -3.4 degrees is not extreme for a Scottish winter, I sized mine on the -10 outside figure.  -10 for a week or more is not unusual here, -18 one night is our record so far.

 

I wonder if the KWh figures they have specified are raw heat input into the building, or kWh of electricity into the ASHP to produce the required heat?

[SteamyTea]

2 minutes ago, Mike_scotland said:

im also assuming the 24552 kWh/year isnt taking into consideration the co officient? so if i got like 2.7/1 or so it would be alot lower?

That is the thermal energy needed to keep your house warm, it is irrespective of the technology.

[Mike_scotland]

1 minute ago, SteamyTea said:

That is to cover the 99th percentile. Almost any heating system will be designed to supply enough power, 99% of the time. That 1% us for extreme weather events i.e. -18⁰C or something.

Most of the time a 6 kW unit would do your heatload quite happily. There is a bit added, 2 kW, for heating the hot water.

So seems to be about the right size.

i think the builder says he was going to go a step up, so its not working too hard or something, is it that bad over sizing?

[SteamyTea]

Just now, Mike_scotland said:

i think the builder says he was going to go a step up, so its not working too hard or something, is it that bad over sizing?

Better to oversize.

Do you have a SAP that shows the heat load, or run it through Jeremy Harris's spreadsheet.

[Mike_scotland]

1 minute ago, SteamyTea said:

That is the thermal energy needed to keep your house warm, it is irrespective of the technology.

JESUS so 25000 kwh a year? thats mental? thats over £5k a year at 0.21p how the hell is that if its a new build

[Mike_scotland]

Just now, SteamyTea said:

Better to oversize.

Do you have a SAP that shows the heat load, or run it through Jeremy Harris's spreadsheet.

the SAP said the house was going to be 8500 all in incl heating.DHW and fans/lightbulbs

[ProDave]

By way of comparison, our ASHP uses just over 1000kWh per year of electricity for DHW heating.  So your figure sounds high.  I wonder how many people they are basing that on?  Granted, in the summer surplus PV does a lot of the DHW heating.

[Mike_scotland]

3 minutes ago, ProDave said:

That means your heat source must be capable of delivering 7.9kW of heat into the house 24/7 on the coldest day.  Assuming you don't want the heating on 24/7 and allowing for DHW heating as well, you will probably be needing a 15kW ASHP at least.  What have they specified?

 

I wonder if the KWh figures they have specified are raw heat input into the building, or kWh of electricity into the ASHP to produce the required heat?

They said a 10kw i think but the builder said he would go for a 13 or 14 so its not running near capacity

[SteamyTea]

Just now, Mike_scotland said:

JESUS so 25000 kwh a year? thats mental? thats over £5k a year at 0.21p how the hell is that if its a new build

That would be if you were heating purely with resistance heating.

Divide by the sCop to get the electric cost.

[Mike_scotland]

Just now, ProDave said:

By way of comparison, our ASHP uses just over 1000kWh per year of electricity for DHW heating.  So your figure sounds high.  I wonder how many people they are basing that on?  Granted, in the simmer surplus PV does a lot of the DHW heating.

[Mike_scotland]

Just now, SteamyTea said:

That would be if you were heating purely with resistance heating.

Divide by the sCop to get the electric cost.

oh i get it now thats more like it, hopefully 2.5 or so atleast bring me down to around 10k

[SteamyTea]

Just now, Mike_scotland said:

oh i get it now thats more like it, hopefully 2.5 or so atleast bring me down to around 10k

SCoP may be higher than 3, does depend on your climate and how hot you have the house.

 

[Mike_scotland]

3 minutes ago, ProDave said:

By way of comparison, our ASHP uses just over 1000kWh per year of electricity for DHW heating.  So your figure sounds high.  I wonder how many people they are basing that on?  Granted, in the summer surplus PV does a lot of the DHW heating.

the next thing im trying to save for is ground solar! or a combination of some on my roof and some on the ground!

[ProDave]

Just now, Mike_scotland said:

oh i get it now thats more like it, hopefully 2.5 or so atleast bring me down to around 10k

10,000kWh after April will cost you about £3K per year.  A LOT of people are going to have a shock at the train wreck that is coming our way.

 

It has never been more important with a new build to insulate, insulate and then insulate a bit more, making it air tight as you go,

[SteamyTea]

1 minute ago, ProDave said:

10,000kWh after April will cost you about £3K

Or 600 quid if on gas.

They are letting us know tomorrow morning what the new rates are, and how they are going to subsidise the increases.

 

[Mike_scotland]

Just now, ProDave said:

10,000kWh after April will cost you about £3K per year.  A LOT of people are going to have a shock at the train wreck that is coming our way.

 

It has never been more important with a new build to insulate, insulate and then insulate a bit more, making it air tight as you go,

yeah im trying to keep on top of it with the builder,

roof has 420mm of wool in the loft
upstairs coombed walls have 150mm of kingspan  then Vapour barrier tin foil stuff then 35mm kingspan over
downstairs has 140mm of frametherm wool then Vapour barrier tin foil stuff then 35mm kingspan over

Ground has UFH with 150mm kingspan and then screed.

probely not the best but its ok i think but not anticipating the energy tripling 

[Mike_scotland]

Just now, SteamyTea said:

Or 600 quid if on gas.

They are letting us know tomorrow morning what the new rates are, and how they are going to subsidise the increases.

 

i would of went gas i think but its country living and i heard ASHP were great and im hoping they are!

[SteamyTea]

Do you know your airtightness numbers?

[Mike_scotland]

1 minute ago, SteamyTea said:

Do you know your airtightness numbers?

they were aiming for the standard 5 but were hoping for better it hasnt been carried out yet... 

i hope thats what you meant m8? 

[ProDave]

1 minute ago, SteamyTea said:

Or 600 quid if on gas.

They are letting us know tomorrow morning what the new rates are, and how they are going to subsidise the increases.

 

Gas will be going up as well in April, quite likely in % terms more than electricity.  Apparently we will know the new cap figure tomorrow.