ASHP Size?

[ashthekid]

I have already decided that we will be having an ASHP installed into my conversion project of an old single skin building dating back to circa 1800’s but with a new timber framed second skin internally and new roof. A good level of insulation in both walls and roof along with triple glazed Velux rooflights and upgraded doubled glazed windows. Total floor space of 385sqm with the ground floor of 240sqm being served by UFH and the 145sqm upstairs being served by radiators. It’s a 5 bedroom, 5 bathroom property housing 4 adults and 1+ children. 
 

My question is what size ASHP should I be aiming for and what size hot water cylinder for this kind of property?

 

I was looking at the LG Therma V split system(low temp version) 12-16kW (as the outdoor unit had to be located approx 30m away from the property - apparently it can be located upto 50m away according to LG website). Would this serve this size property and potential demands?

[Nickfromwales]

5 bathrooms, so each room to have either a bath / shower or combo? One just a cloakroom WC? Specific details are needed for advice on capacity / size / type of cylinder  Number of showers per day, time they are taken, same with baths. Kitchen and utility.

The size of the heat pump needs a LOT more info, eg heat loss calcs / DEPC and location / climate etc.

INPUT!!  

Edited April 18, 2021 by Nickfromwales

[SteamyTea]

And it will probably need more than 1 ASHP in reality.

What size water and electrical connections do you have?

Edited April 18, 2021 by SteamyTea

[ashthekid]

Location is north Hampshire.

5 bathrooms consisting of 3 with just showers & 1 with just a bath and one with both a bath and a shower. Two of the bathrooms will be just spare unused room en-suites. All 5 with WC’s. There is also an additional cloakroom WC with just a WC so 6 WC’s in total. Likely usage to be 2/3 showers a day. Rarely use baths at all to be honest so wouldn’t include them in usage. 

One kitchen and one kitchenette. Including the pantry and utility room there are 4 sinks(excluding bathrooms).

 

I have not done any heat loss calcs, never done that before. Just in the middle of getting SAP calcs tho. 

[ProDave]

It would be a lot better if you had UFH upstairs then all the heating requirement would be low temperature water.

[ashthekid]

That is a valid point although it’s going to be fully carpeted(excluding bathrooms) and I was under the impression UFH isn’t as efficient or good under carpet. 

Edited April 18, 2021 by ashthekid

[SteamyTea]

21 minutes ago, ashthekid said:

That is a valid point although it’s going to be fully carpeted(excluding bathrooms) and I was under the impression UFH isn’t as efficient or good under carpet. 

There are a number of ways to transfer energy, only one of them is with a higher temperature.

You can increase amount of pipework (reduce the spacing) in the UFH and still deliver the same power.

There is a difference between energy, power and temperature.

[Nickfromwales]

1 hour ago, ashthekid said:

That is a valid point although it’s going to be fully carpeted(excluding bathrooms) and I was under the impression UFH isn’t as efficient or good under carpet. 

What standard are you building to? Current regs with trickle vents? Box tick amount of insulation? Builder in on price so wants to get in and out? 
Ventilation heat loss from excessive infiltration is the enemy, more so than insulation in actuality.

You can use UFH under carpet upstairs with good results as long as you fit a manifold dedicated to each discipline, eg one downstairs and one upstairs so each can have individual flow temps. Upstairs will need a higher flow temp to combat the TOG ratings. 
Having all GF UFH will convey a good bit of heat to upstairs, but is dependant on the layout, eg open plan hall / stairs / landing promotes this. 
Build to a good standard and you’ll find few of the upstairs rooms need big numbers for additional heating anyways, build poorly and the UFH may never get them up to temp ( unless left on 24/7 on ‘setback’ temp and then jumping via programming to ‘comfort’ for anticipated occupancy ). 
Cn be done with aluminium spreader plates between joists, just you’ll need the joists at 400mm centres to get the plates in between. Lining up the joists either side of steels / glulams helps a lot if they create intersections  in the same room.

Radiators = simple. UFH = pita, but well worth the effort in the end.