Help with solar pv

[Mike_scotland]

1 minute ago, SteamyTea said:

No, I am on E7.  So resistance heating.

The grey columns shows my usage (two charts up), but if I had an ASHP, the heating time could easily be shifted by 10 hours.

totally makes sense now mate, so even with just a few hours E7 elecy to heatup your water it stays hot most of the day! 

[Mike_scotland]

2 minutes ago, ProDave said:

Yes exactly that.  the ASHP is set to start heating DHW at 11AM (to ensure there should be reasonable PV generation by then) and shuts off when it gets to 48 degrees.  Any surplus PV after that, and the immersion heater soaks up the excess heating the water hotter.

 

In the summer, often there is enough just from the immersion heater that the ASHP does not turn on because by 11AM it is already up to 48 degrees.

 

sounds like the penny has dropped mate haha!, im all new to this but i love learning new things and want to learn.

makes sense to do that definitely. so what do you have an 10kw ashp and 4kw solar panels?

i think my builder has stated a 12kw ashp for me its a 230m2 house.

[SteamyTea]

Just now, Mike_scotland said:

totally makes sense now mate, so even with just a few hours E7 elecy to heatup your water it stays hot most of the day! 

Yes.

That is down to decent insualtion.

I added extra to mine as when I changed it I had to get a like for like replacement.

Some people have gone down the Sunamp DHW storage system as the losses are very low, but they cost a lot more than a cylinder.

If you are not totally committed in your house design yet, consider fitting the cylinder in a larger cupboard so that extra insulation can be added.

[Mike_scotland]

1 minute ago, SteamyTea said:

Yes.

That is down to decent insualtion.

I added extra to mine as when I changed it I had to get a like for like replacement.

Some people have gone down the Sunamp DHW storage system as the losses are very low, but they cost a lot more than a cylinder.

If you are not totally committed in your house design yet, consider fitting the cylinder in a larger cupboard so that extra insulation can be added.

 

i think our hot water cylinder will be inside a large cupboard at the back of the garage but the cupboard is to be well sheeted out with insulation for that exact reason to keep it warm in there, i think that is were it is going anyway on the plans we have a designated space for equipment etc for all the stuff the ASHP presumably comes with

[SteamyTea]

2 minutes ago, Mike_scotland said:

i think my builder has stated a 12kw ashp for me its a 230m2 house.

The actual physical size of the house is irrelevant, it is how much energy it uses and the peak power needed (that kWh and kW thing again).

 

It is usual to oversize ASHPs as they produce a better CoP (the performance multiplier) that way.

Think of it as a car, gently cruising along a deserted road the fuel economy is quite good, but accelerate up a hill and it drops significantly.  In car terms it is know as the specific brake fuel consumption and often larger engine cars produce better fuel economy (it is to do with the cylinder area to power ratio).

[Mike_scotland]

1 minute ago, SteamyTea said:

The actual physical size of the house is irrelevant, it is how much energy it uses and the peak power needed (that kWh and kW thing again).

 

It is usual to oversize ASHPs as they produce a better CoP (the performance multiplier) that way.

Think of it as a car, gently cruising along a deserted road the fuel economy is quite good, but accelerate up a hill and it drops significantly.  In car terms it is know as the specific brake fuel consumption and often larger engine cars produce better fuel economy (it is to do with the cylinder area to power ratio).

 

sorry its 14kw i just re read an email.

yeah sort of makes sense, so if my house was double the size but airtight(as an example) the heat pump could well be even less kw?

[Mike_scotland]

9 minutes ago, SteamyTea said:

Yes.

That is down to decent insualtion.

I added extra to mine as when I changed it I had to get a like for like replacement.

Some people have gone down the Sunamp DHW storage system as the losses are very low, but they cost a lot more than a cylinder.

If you are not totally committed in your house design yet, consider fitting the cylinder in a larger cupboard so that extra insulation can be added.

going back to what i said before, we have a plant room its roughly 1m by 2.5m.

[SteamyTea]

2 minutes ago, Mike_scotland said:

so if my house was double the size but airtight(as an example) the heat pump could well be even less kw

Yes, this is why older houses tend to use a lot of energy.

They leak air and the insulation levels are very low.

[SteamyTea]

1 minute ago, Mike_scotland said:

roughly 1m by 2.5m.

Not that big, it is the 1m size that will limit the amount of insulation.  Can you make it 1.5m?

[Mike_scotland]

1 minute ago, SteamyTea said:

Not that big, it is the 1m size that will limit the amount of insulation.  Can you make it 1.5m?

i think possibly as it will just take a bit of space from the garage, i will discuss with the builder as you are correct in what you are saying, and im a bit panicking about the rising cost of elecy and my whole house is electricity.

[SteamyTea]

2 minutes ago, Mike_scotland said:

i will discuss with the builder

Then get a stick, beat into him that airtightness and properly fitted insulation are important.

Then beat him again.

And again.

And again just in case.

 

Tell him that if you don't get an airtightness number of below 0.5 ACH, then you will send him your electricity bill every month.

Then beat him again.

[Mike_scotland]

Just now, SteamyTea said:

Then get a stick, beat into him that airtightness and properly fitted insulation are important.

Then beat him again.

And again.

And again just in case.

 

Tell him that if you don't get an airtightness number of below 0.5 ACH, then you will send him your electricity bill every month.

Then beat him again.

hahahaha its going to be some size of stick hes twice the size of me!!
 

what is a good air tightness to realistically be looking at? to get 0.5 is that not very low?

[IanR]

42 minutes ago, Mike_scotland said:

what is a good air tightness to realistically be looking at? to get 0.5 is that not very low?

For someone looking for low energy losses, but not wishing to go as far as PassivHaus type measures then 3m³/m².H @50 Pa is the sweet spot. (I've changed units from ACH as "m³/m².H @50 Pa" this is what Building Regs uses)

In England at least, if you drop below this level then Building Regs require you to provide mechanical ventilation, which you're not going to benefit from unless you go significantly below this threshold.

Edited September 27, 2021 by IanR

[Mike_scotland]

1 minute ago, IanR said:

For someone looking for low energy losses, but not wishing to go as far as PassivHaus type measures then 3m²/m³.H @50 Pa is the sweet spot. (I've changed units from ACH as "m²/m³.H @50" this is what Building Regs uses)

In England at least, if you drop below this level then Building Regs require you to provide mechanical ventilation, which you're not going to benefit from unless you go significantly below this threshold.

i think my SAP calcs and builder was saying hes aiming for 4 minimum, but i hope we get lower and i will see what we can do at this stage to guarantee 3.

[ProDave]

9 minutes ago, Mike_scotland said:

i think my SAP calcs and builder was saying hes aiming for 4 minimum, but i hope we get lower and i will see what we can do at this stage to guarantee 3.

I think 4 is generally used as a default value in design SAP calculations.  Mine came out at 1.4, I would have preferred less but it is what it is.

[Mike_scotland]

1 minute ago, ProDave said:

I think 4 is generally used as a default value in design SAP calculations.  Mine came out at 1.4, I would have preferred less but it is what it is.

how did you get it so low Dave? 

any tips i can do or say to my builder(he should already know, i know) but builders are builders.... hes taping the insulation i know that

[ProDave]

14 minutes ago, Mike_scotland said:

how did you get it so low Dave? 

any tips i can do or say to my builder(he should already know, i know) but builders are builders.... hes taping the insulation i know that

The entire inside of the timber frame is lined with an air tightness membrane, all joints sealed with air tight tape.  All penetrations sealed, air tight membrane taped to all windows and doors.  The key thing is attention to detail.

 

 

One thing you need to think about at frame up time is sealing the joist ends at first floor.  I used a "Tony tray" which is a strip or membrane that exits the frame, round the outer end of the joists and then back in, and then taped to the rest of the membrane.

[SteamyTea]

9 minutes ago, Mike_scotland said:

hes taping the insulation i know that

Well that will look like it is doing something.

 

It is general quality of work.

Attention to detail everywhere, not what is just easy to see and do.

If you are building a brick or block place, are you getting the walls parge coated? No good relying on plaster to stop the air leaks, it is in the wrong side of the insulation.

[Mike_scotland]

12 minutes ago, SteamyTea said:

Well that will look like it is doing something.

 

It is general quality of work.

Attention to detail everywhere, not what is just easy to see and do.

If you are building a brick or block place, are you getting the walls parge coated? No good relying on plaster to stop the air leaks, it is in the wrong side of the insulation.

we are TF house mate with a render outer leaf breeze block.

[Mike_scotland]

13 minutes ago, ProDave said:

The entire inside of the timber frame is lined with an air tightness membrane, all joints sealed with air tight tape.  All penetrations sealed, air tight membrane taped to all windows and doors.  The key thing is attention to detail.

 

 

One thing you need to think about at frame up time is sealing the joist ends at first floor.  I used a "Tony tray" which is a strip or membrane that exits the frame, round the outer end of the joists and then back in, and then taped to the rest of the membrane.

very nice that Dave. looks a good job.

[SteamyTea]

17 minutes ago, Mike_scotland said:

we are TF house mate with a render outer leaf breeze block.

Then glue or tape everywhere outside air can get through. Then tape the insulation into place (why did you not go for celluloses, that insulates are fills holes up.

Then when the vapour control layer is fitted, tape that up, including all penetrations, no matter how small i.e external light cable, telephone wire.

Then make sure that nothing gets damages or pierced when finishing the rest.

Plumbers don't care about airtightness, so watch them carefully.

[Mike_scotland]

Just now, SteamyTea said:

Then glue or tape everywhere outside air can get through. Then tape the insulation into place (why did you not go for celluloses, that insulates are fills holes up.

Then when the vapour control layer is fitted, tape that up, including all penetrations, no matter how small i.e external light cable, telephone wire.

Then make sure that nothing gets damages or pierced when finishing the rest.

Plumbers don't care about airtightness, so watch them carefully.

i think we are 150mm of wooltherm or whatever it is called then 40mm of PIR insulation on top then taped the butts.

[SteamyTea]

1 minute ago, Mike_scotland said:

i think we are 150mm of wooltherm or whatever it is called then 40mm of PIR insulation on top then taped the butts.

That can hide a lot of sins, and holes.

You need to make sure that the exterior, OSB I am assuming, is airtight. That is where the losses happen.

And, as @ProDave said, at the top and bottom of the walls. Especially true if the roof is a cold one.

Between floors, that space between a ceiling and floorboards, where it meets the walls is the tricky bit. 

 

I hope that not too much insulation has been fitted before you can check. 

[Mike_scotland]

26 minutes ago, SteamyTea said:

That can hide a lot of sins, and holes.

You need to make sure that the exterior, OSB I am assuming, is airtight. That is where the losses happen.

And, as @ProDave said, at the top and bottom of the walls. Especially true if the roof is a cold one.

Between floors, that space between a ceiling and floorboards, where it meets the walls is the tricky bit. 

 

I hope that not too much insulation has been fitted before you can check. 

i think its OSB , can it be plywood or similar?

[SteamyTea]

15 minutes ago, Mike_scotland said:

i think its OSB , can it be plywood or similar?

Yes.

 

The thing to remember is that you need to stop cold, outside air, blowing across/through the insulation.

If air flows across/through insulation, it is the same as having a greater wall area to loose energy through.