Heat loss calcs, no 1st floor heating

[Barnboy]

I'm still to get an air test, not cheap and I'm not air tight yet.

I've filled in Jeremy's heat loss calculator, to try and get an idea of ashp and ufh sizing.

Firstly I'm not 100 % sure which figures I should be using fromt eh calculator to work these things out as there's

Total heat loss,

Inside vs outside heat loss,

Total daily min and average, 

I had someone round to look at giving me a price for them to supply and fit, and also which would be the best position for a unit and route for pipework into the house.

The guy did a rough calc on his phone of 40w/m²  for ufh  multiplied by 90 for the m² footprint of the building, saying I then needed 3.6kw ashp capacity,

He then said as I have no heating on the 1st floor, only power points if I did want to put panel heaters in the future, I'd need to double the capacity of the heat pump.

Is his theory correct that I'd need to double up having no upstairs heating,  and which figure on the calc do I use ?

Thanks 

[nod]

We have radiators in the bedrooms that we will never use But the HP guy did the same with us If the rads are there They May need a heat supply 24-7 

Weve put them in with any future sale in mind As some people assume all bedrooms are going to be cold in winter 

I’d stick to your original plan 

[JohnMo]

You use, the Daily heat loss power for min OAT the coldest day. In thee example below for Jan.

 

 

So that gives you the total heat loss for your house.

22 minutes ago, Barnboy said:

I'd need to double the capacity of the heat pump.

Is his theory correct

No. Total heat loss is total heat loss, if this is supplied by 100 or 1 heater it's still the same.

[Barnboy]

So I'd be looking at needing a 4kw, or the nearest above that ashp if my calls attached are correct?

[ProDave]

There is an even simpler way

 

I did not bother looking up the OAT data for my location so I only filled in the spreadsheet down as far as row 70

 

so row 70 column H shows me with a delta t of 30 degrees (20 degrees inside, -10 outside)  the calculated heat loss is 2310 watts.  So on the coldest day in winter my heating needs to put 2310W of heat into the building.

 

Why make it any more complicated?

 

 

 

[JohnMo]

27 minutes ago, Barnboy said:

So I'd be looking at needing a 4kw, or the nearest above that ashp if my calls attached are correct?

So your area never freezes, you have a min temp of 0.6.

 

You should really follow what @ProDave says or use these instructions as a sizing guide

 

[Barnboy]

I got the weather data from the local met office when I had to get the u-value calculations done for my bco.

I'm in sunny Jersey ☀️ although the ashp would face east with nothing between it and a good easterly blowing in from France.

I'll ready through those papers later when I can see them on a bigger screen.

Thank you.

[JohnMo]

10 hours ago, Barnboy said:

although the ashp would face east with nothing between it and a good easterly blowing in from France.

That makes no difference, except make sure it's a heat pump suitable for a coastal location.

[Barnboy]

8 hours ago, JohnMo said:

That makes no difference, except make sure it's a heat pump suitable for a coastal location.

Does wind chill not affect the performance ?

If an ashp was facing south in a sheltered location on a sunny winters day with a chilly easterly wind would it not perform better than if it was in a shaded spot with the wind blowing straight at it ?

[Kelvin]

1 hour ago, Barnboy said:

Does wind chill not affect the performance ?

If an ashp was facing south in a sheltered location on a sunny winters day with a chilly easterly wind would it not perform better than if it was in a shaded spot with the wind blowing straight at it ?

It’s more the ambient temperature around the ASHP which doesn’t vary much around a building as I understand it. 

[Kelvin]

Like many on here we haven’t put rads upstairs but have wired for panel heaters. I hate radiators anyway. Ugly things that take up space. I get the argument that says fit them for when you come to sell but we’ve built our house for us not the next owners. I did contemplate taking pipework upstairs for radiators so that rads could be added later but didn’t. The temperature in the upstairs rooms is perfect for us so far but yet to fit doors. 

[SteamyTea]

It is an interesting point about windchill.

Windchill is caused by evaporation, which is a phase change, and with water, a huge shift in energy levels, around 540 times different.

If it was a problem, ASHP would not work a lot of the time.

There may be marginal conditions where a 'triple point' temperature happens (ice, liquid and gas), but I doubt it as air pressure is probably too high.

 

As for, as mentioned on another post, cold air recirculating back into the unit, without putting the unit into a well insulated, close fitting, airtight box, I don't think this is an issue.  The amount of air a heat pump shifts is pretty minor compared to the amount of air surrounding it.

Edited April 15 by SteamyTea

[JohnMo]

2 hours ago, Barnboy said:

Does wind chill not affect the performance ?

If an ashp was facing south in a sheltered location on a sunny winters day with a chilly easterly wind would it not perform better than if it was in a shaded spot with the wind blowing straight at it ?

As above, also the unit is pulling a huge volume of air through it, so it's making its own strong wind.

 

(Bold section) No

[ProDave]

My ASHP is on a south facing wall.  In winter on a still day here, the front of the house that does not get any sun can stay cold and frosty all day long.  The south that gets any sun going, warms up and the frost melts.

 

I cannot believe being on the warmer side of the house has no positive effect on the ASHP performance.

[Kelvin]

Once the fan starts running it cools the air anyway so whatever the benefit might be on the sunny side of the building will be lost. Length of pipe runs to the manifold matters more. 

[dpmiller]

^ I'm with @ProDave on this, any bit of solar gain is good, even if it just shaves a few seconds off a defrost...

[joe90]

18 minutes ago, ProDave said:

cannot believe being on the warmer side of the house has no positive effect on the ASHP performance.

Certainly would help defrost in the sunshine!,

1 hour ago, Kelvin said:

upstairs but have wired for panel heaters.

Electric heaters usually have three pin plugs so I just made sure sockets were in a suitable location.

[Kelvin]

34 minutes ago, dpmiller said:

^ I'm with @ProDave on this, any bit of solar gain is good, even if it just shaves a few seconds off a defrost...

Measure the air temperature around your building on a sunny day. I think people get fooled because shaded areas feel cooler despite the air temperature being much the same. When siting an ASHP the sun is the least important factor. 

Edited April 15 by Kelvin

[SteamyTea]

2 minutes ago, Kelvin said:

I think people get fooled because shaded areas feel cooler despite the air temperature being much the same.

Yes, it is the radiative forcing of sunlight.  Not unusual to be 1000W/m², it can be like standing directly in front of a fan heater.

[joe90]

Well my car defrosts (one side) when the sun is shining on it (not saying it improves an ASHP,s efficiency just defrosting) however my ASHP was on a western wall and after the sun was shining on the brickwork it radiated heat back at you.. like @ProDave I think it would make a little difference and had planned to time it to run from 11am so the ambient temp was likely to be a little higher.

[JohnMo]

Evaporator is on the wall side of the heat pump, so always in the shade, sun would never get close to the area to be effective with aiding defrost.

 

Your heat pump reads the air temperature it sees going via the evaporator, compare it to ambient on a sunny day and report. Mine is exposed to early sun, if it's cold and sunny the air going through the evaporator is also cold.

[Bramco]

3 hours ago, Barnboy said:

Does wind chill not affect the performance ?

 

As above, probably not on the ASHP but surely the 'feels like' temperature, often windchill but sometimes just a clear sky at night, must make a difference to the heat required by the house. We've been monitoring the 'feels like' temperature recently and on some nights it can be at least 5C below the actual OAT. You can see this on the graph below.

 

So the question then becomes, should you, in the spreadsheet use an OAT which is 5C or so below what the met office tell you is the lowest OAT? Which would mean a bigger heat pump than the spreadsheet would normally indicate.

 

We're going to use the data to create some kind of 'heat required index' for our build and use that to set how long the ASHP runs for.

 

Simon

 

If you look at the 10th and 14th you can see the feels like temperature drops by about 5C from the outside temperature. Green and Yellow lines. The data is from openweathermap.

 

[Thorfun]

2 hours ago, Kelvin said:

Like many on here we haven’t put rads upstairs but have wired for panel heaters. I hate radiators anyway. Ugly things that take up space. I get the argument that says fit them for when you come to sell but we’ve built our house for us not the next owners. I did contemplate taking pipework upstairs for radiators so that rads could be added later but didn’t. The temperature in the upstairs rooms is perfect for us so far but yet to fit doors. 

i also didn't put any central heating upstairs and i was worried as i'd never lived in a house where that was even possible! but fearing overheating we did put in AC so that could be used for heating if required. i doubt it ever will be. yesterday we were working in the house and the sun was coming through the windows and we had to actually turn the AC on to cool the rooms and it's only April. granted we were plumbing so it might've been ok for just sitting around in but i am now convinced that cooling is more important upstairs than heating in our house.

[SteamyTea]

1 hour ago, Thorfun said:

it's only April

Yesterday, in London, the sun got to 48.01° above the horizon.

June 21 it will be at 61.93°, December 21 15.06°.

 

You may find that the height of summer is not so bad.

[ProDave]

Another point about Jeremys spreadsheet.  The last part, where he inputs OAT data and predicts monthly heating requirement is flawed.  If I look at the figures I have, which still has the OAT data for where Jeremy lives which is a lot milder than here, it gives me monthly values way higher that reality.

 

In particular I find OAT of 10 degrees is a tipping point for us.  10 degrees or more and we don't need any heating at all.  Yet Jeremy's spreadsheed is still calculating a June / July / August heat loss where nobody will be using any heating.