Heat loss calculators

[keyser]

I'm sure I'm wrong but if heat pumps generally don't do zoning for efficiently reasons, then the house/flat could just be treated as one big room for heat loss calculations? Just remove all internal walls and add up the roof, window space, or this will just give me a total for the property, not what size rads each room will need - assuming all the doors are closed and heat doesn't mix between each room?  As Seinfeld says, that's about as likely as the coffee and milk to stay separate in a mug!

 

But I do admit that my kitchen is a cold room, maybe 19C when the rest of my flat is 20/21C, that means my kitchen fire door has a fair amount of insulation effect. Anyway, my kitchen rad wasn't spec'd right when the council fitted it for that room, they just whacked a rad on the easiest wall and job done.

 

These heat loss calculators are designed with a certain outside temperature in mind I take it? I've often heard to design around -3C outside, as that is a typical winter temperature, but does that mean it'll need an extra 1-2kw in the system (heat pump, pipe diameter, rads) to make sure it's able to go some way past that? -5C -7C? I haven't tried to use the heat loss calc spreadsheet that is posted here sometimes, as when I opened it my face melted off.

Edited May 5, 2022 by keyser

[ProDave]

8 minutes ago, keyser said:

These heat loss calculators are designed with a certain outside temperature in mind I take it? I've often heard to design around -3C outside, as that is a typical winter temperature, but does that mean it'll need an extra 1-2kw in the system (heat pump, pipe diameter, rads) to make sure it's able to go some way past that? -5C -7C? I haven't tried to use the heat loss calc spreadsheet that is posted here sometimes, as when I opened it my face melted off.

If you want to do it accurately, that is the calculator to use, but you do need a good understanding of the makeup of the building to work out the U values of the walls etc.

 

Heating with an ASHP can be zoned like any other heating system, we have 3 zones for the 3 rooms downstairs, but in practice there is little variation room to room.  Many don't bother and treat it as just one big room.

 

i calculated our heating load for an outside temperature of -10 which is actually common for a week or more in winter up here, sometimes even longer, -18 being the coldest night I have recorded so far.  You won't get that cold where you are of course.

[SteamyTea]

3 minutes ago, ProDave said:

-18 being the coldest night I have recorded so far.  You won't get that cold where you are of course.

Was -16⁰C here once.

https://www.cornwalllive.com/news/cornwall-news/times-cornwall-recorded-extreme-weather-6532125 

[HughF]

I used the one from freedom heat pumps, which does have a few issues in the output data for the midea units and in the rad sizing sheet (rad sizing is designed for a fixed 50 deg flow temp, even though the performance sheet allows you to change the flow temp).

 

I designed for a 21 deg room temp at -3.5 outdoor temp. It rarely gets that cold where we are and I’m oversizing the unit ‘a bit’.

[keyser]

Beast from the East in Birmingham was -7C I think, that should probably do me.

[HughF]

I used the one from freedom heat pumps, which does have a few issues in the output data for the midea units and in the rad sizing sheet (rad sizing is designed for a fixed 50 deg flow temp, even though the performance sheet allows you to change the flow temp).

 

I designed for a 21 deg room temp at -3.5 outdoor temp. It rarely gets that cold where we are and I’m oversizing the unit ‘a bit’.

[keyser]

Yeah either -7C outside and flow temp of 50C or -3C outside and flow of 40C probably translates into the same thing. I assume the rule of installing the largest radiators possible applies either way.

[ReedRichards]

If you are doing the MCS heat loss calculation then the outdoor temperature is whatever it is warmer than for 99.6% of the time.

[HughF]

1 hour ago, keyser said:

Yeah either -7C outside and flow temp of 50C or -3C outside and flow of 40C probably translates into the same thing. I assume the rule of installing the largest radiators possible applies either way.

A-7/W50 is a much harder task than A-3/W40…. Much harder. Rad sizing at 50 deg flow is Easier, but I’d try and size for 45 if you can.

[HughF]

Attached, the unlocked/unhidden version of the Freedom toolkit.

 

They were giving this to anyone who asked for it, off the back of a youtube video showing how it worked, but that video has now been taken down.

2124036581_2021FreedomHeatPumpstoolkitV3.3forallinstallers-Copy.xlsx

[keyser]

I went by the Heat Geek youtube guys, their cheat sheet calculations for type 21 radiators @ 40C flow is 800W/m2, and 1140W/m2 for 50C flow. Of course they also say get a proper heat loss survey done which I will as I know that's necessary.

 

Then I went on Plumbingnation calc and a few others and they all pretty much said the same thing, so I took that value and increased by 20%.

 

Based on that its just a case of biggest radiators I can fit in, which I can. I don't actually need type 22 rads except in the kitchen. Surely if the system is designed around 40C flow then there is capacity to increase until the heat pump reaches maximum heat output of say 55C? The COP will go down but only 0.4% of the time.

 

Surely I'm not the first person that owns a 1960s ex-council flat to install a heat pump? or maybe I am  The same building can just be copy/pasted to the correct location in the UK and boom, heat loss calculated?

 

Anyway the first problem I have is what option do I enter as 1960s walls, not cavity filled? or just fast forward to 'I will get those filled before the heat pump is installed'? And there is a heated flat above me so what do I put in as the roof?

 

Thanks

Edited May 6, 2022 by keyser

[SteamyTea]

29 minutes ago, keyser said:

 

Anyway the first problem I have is what option do I enter as 1960s walls,

Just look up the thermal conductivity of the materials used, divide into their thickness, then divide into 1.

Round up 

Edited May 6, 2022 by SteamyTea

[HughF]

1 hour ago, keyser said:

I went by the Heat Geek youtube guys, their cheat sheet calculations for type 21 radiators @ 40C flow is 800W/m2, and 1140W/m2 for 50C flow. Of course they also say get a proper heat loss survey done which I will as I know that's necessary.

 

Then I went on Plumbingnation calc and a few others and they all pretty much said the same thing, so I took that value and increased by 20%.

 

Based on that its just a case of biggest radiators I can fit in, which I can. I don't actually need type 22 rads except in the kitchen. Surely if the system is designed around 40C flow then there is capacity to increase until the heat pump reaches maximum heat output of say 55C? The COP will go down but only 0.4% of the time.

 

Surely I'm not the first person that owns a 1960s ex-council flat to install a heat pump? or maybe I am  The same building can just be copy/pasted to the correct location in the UK and boom, heat loss calculated?

 

Anyway the first problem I have is what option do I enter as 1960s walls, not cavity filled? or just fast forward to 'I will get those filled before the heat pump is installed'? And there is a heated flat above me so what do I put in as the roof?

 

Thanks

I’d fit type 22s as a matter of course, this whole ‘get by with what you’ve got because we can just turn the flow up to 55’ mentality that lazy specifiers seem to have is half of the problem with domestic heat pumps here on the UK. Specifiers should be designing for a 45 deg flow when using rads in my opinion.

 

But yeah, basically just fit the biggest type 22 you can in each room and you’ll be sorted. If the rooms are too hot just turn the flow temp down and watch the cop rise.

 

As for the walls, the heat loss calc has an entry for ‘custom’ rather than ‘from data entry’ where you can enter a specific U value.

 

As you are in a flat, put every room as ‘heated room above’ on the drop down box.

[keyser]

My estimate plumbingnation calc +20% was 4015 watts. My heat loss from that spreadsheet is 4019 watts. boom science, I mean boom guessing :). I did find more options in the drop downs in the end. So if my heat loss is 4kw does that mean I should spec to a 6kw heat pump for the extra 2 days a year on average it'll be below -3.7C?

Edited May 6, 2022 by keyser

[HughF]

2 hours ago, keyser said:

My estimate plumbingnation calc +20% was 4015 watts. My heat loss from that spreadsheet is 4019 watts. boom science, I mean boom guessing :). I did find more options in the drop downs in the end. So if my heat loss is 4kw does that mean I should spec to a 6kw heat pump for the extra 2 days a year on average it'll be below -3.7C?

Play with the 'your system' tab on the spreadsheet and have a look at what machines around the 5-6kW bracket will cover the heat load (you can specify the UVC size in this section too). Beware, some manufacturers ratings in the model numbers don't really add up in reality (cough, Midea, LG, cough)... Midea won't sell you one anyway, so you can discount them.

 

5kW ecodans pop up on eBay fairly often, usually with the 150ltr pre-plumbed cylinder package.

[keyser]

16 minutes ago, HughF said:

Play with the 'your system' tab on the spreadsheet and have a look at what machines around the 5-6kW bracket will cover the heat load (you can specify the UVC size in this section too). Beware, some manufacturers ratings in the model numbers don't really add up in reality (cough, Midea, LG, cough)... Midea won't sell you one anyway, so you can discount them.

 

5kW ecodans pop up on eBay fairly often, usually with the 150ltr pre-plumbed cylinder package.

OK thanks. Should I buy from ebay? I'd want to make sure I've got all the warranty and support for it. Have spotted the Ecodan's ticks all the boxes (quiet), except the thread about 200 idle vampire watts. I want 200 vampires to be busy not idle etc.

Edited May 6, 2022 by keyser

[HughF]

5 minutes ago, keyser said:

OK thanks. Should I buy from ebay? I'd want to make sure I've got all the warranty and support for it. Have spotted the Ecodan's ticks all the boxes (quiet), except the thread about 200 idle vampire watts. I want 200 vampires to be busy not idle etc.

Buy from wherever you feel comfortable. We all have a different appetite for risk, mine seems quite large

 

You're unlikely to get any warranty if someone installs it who isn't 'manufacturer approved' - or some similar rubbish. Personally, I'd just buy it and find a friendly, decent, local plumber to hook it up. If your technically minded enough, the installer settings are pretty damn simple on most of these things, just a few temp and time settings. You basically can't screw them up.

[ReedRichards]

8 hours ago, keyser said:

... So if my heat loss is 4kw does that mean I should spec to a 6kw heat pump for the extra 2 days a year on average it'll be below -3.7C?

 

Well you need to allow a certain amount of margin for when your heat pump is heating your hot water and not your house.  And when it is defrosting in cold weather.  Also consider whether you want to turn it off at night or keep it running 24/7.