Cooling options

[Nicolas]

We have started on a bungalow project in southern England. It will have south-east facing living areas and additional glazing on the south-western side - all posing an overheating risk without external shading, which will be added.

 

The building will have:

• MVHR
• ASHP for UFH and DHW. No radiators.
• Solar array and battery.

 

I'm considering cooling options and quotes.

1. Underfloor cooling with appropriate sensors - is it worth the condensation risk and additional cost? Excluding plumbed rooms, we may have wooden flooring throughout.
2. Adding fan coils vs a separate air-to-air heat pump and split system? The latter is coming out cheaper so far, which seems counterintuitive. We have space for a heat pump of each type.

 

[Nickfromwales]

2 hours ago, Nicolas said:

We have started on a bungalow project in southern England. It will have south-east facing living areas and additional glazing on the south-western side - all posing an overheating risk without external shading, which will be added.

 

The building will have:

• MVHR
• ASHP for UFH and DHW. No radiators.
• Solar array and battery.

 

I'm considering cooling options and quotes.

1. Underfloor cooling with appropriate sensors - is it worth the condensation risk and additional cost? Excluding plumbed rooms, we may have wooden flooring throughout.
2. Adding fan coils vs a separate air-to-air heat pump and split system? The latter is coming out cheaper so far, which seems counterintuitive. We have space for a heat pump of each type.

 

Hi. 
 

We’ll need some more info, eg airtightness target, construction methodology, foundation type, etc etc to give the most robust advice   

 

“Input!”  

[IanR]

More info would definitely help.

 

I have the same orientation and solar gain risk, and I'm also single storey. External Blinds are very effective.

 

With the greater contribution roof insulation gives in a bungalow I'd also suggest high decrement delay insulation. Something like blown cellulose insulation.

 

If you're having UFH then cooling via the ASHP is a no brainer. It's the cost of a controller that can handle cooling as well as heating and is effective at just above dew point temps so no risk of condensation.

 

I would also add either air to air heat pump cooling or fan coils in the main rooms. If you have space for the second heat pump then go air to air, as the fan coils, I assume, would be better with a  lower flow temp than your UFH cooling needs.

Edited 22 hours ago by IanR

[Nicolas]

1 hour ago, Nickfromwales said:

We’ll need some more info

Treated floor area - 156m² (73 renovation + 83 extension)

Masonry floors and walls. Cavity and under-screed insulation.

Extension/renovated roof: 0.14; 0.15 W/m²k. Floors: 0.11; 0.28 W/m²k. Walls: 0.14; 0.3 W/m²k
Planned airtightness - 1.6 m³/hr.m²
Space heating demand -  49 kWh/(m².a)

Heat load - 22 W/m²
Heating requirement - 3.5 kW (+ domestic hot water)

 

Thanks

Edited 21 hours ago by Nicolas

[Nicolas]

1 hour ago, IanR said:

If you're having UFH then cooling via the ASHP is a no brainer.

Thank you! That's very reassuring. I think we'll put tiles over the UFH zone under the living areas in the extension and wood over the zone in the bedrooms located in the original building. Aircon to the bedrooms could top up the heating if it's ever necessary.

Edited 21 hours ago by Nicolas
Clarity

[Nicolas]

1 hour ago, IanR said:

If you have space for the second heat pump then go air to air, as the fan coils, I assume, would be better with a  lower flow temp than your UFH cooling needs.

There's a workaround for that (had a long conversation with an ASHP installer on the subject - additional buffer tank I think).

 

It seems a waste not to use the heat pump we are getting anyway for active cooling, but if it costs more, we'll just get an air-to-air one in addition. I suppose that it would provide some redundancy if the A2W one stopped working.

[JohnMo]

9 hours ago, Nicolas said:

Underfloor cooling with appropriate sensors

You don't need any additional sensors, just run above dew point then zero issues.  Dew point depends on house temperature.  But generally you can run 14 to 16 degs without issue.

 

4 hours ago, Nicolas said:

additional buffer tank

You don't need a buffer let alone another one.  Run it all single zone. Unless you have a real reason to run multiple zones.

 

9 hours ago, Nicolas said:

Adding fan coils

Two types of fan coils, one designed for below dew point and others that don't.  The ones that don't are cheaper and you can run same temp as UFH flows so have a simple system.

5 hours ago, Nicolas said:

domestic hot water

Just do direct heating, save money buying a heat pump cylinder and heat on ToU tariff. Then you can run heating and DHW in cheap periods.

[Oz07]

9 hours ago, JohnMo said:

 

Just do direct heating, save money buying a heat pump cylinder and heat on ToU tariff. Then you can run heating and DHW in cheap periods.

Are normal cylinders a lot cheaper than heat pump ones? Are they "vented" or "unvented" or doesn't this change with direct heating? Can an immersion heater recharge the water temperature as quick as a heat pump? Why would heat pump cylinder stop you heating it in cheap period?

[JohnMo]

Heat pump cylinder is more expensive, vented or unvented is a design choice doesn't matter how it's heated.  Unvented runs the cylinder at approx 3 bar, vented has a tank in the loft to supply the pressure. 

 

25 minutes ago, Oz07 said:

Can an immersion heater recharge the water temperature as quick as a heat pump?

Depends on size of immersion and size of heat pump and how it's set up.

 

26 minutes ago, Oz07 said:

Why would heat pump cylinder stop you heating it in cheap period?

It doesn't, but with a heat pump you are EITHER heating house or cylinder, not both.  So if cylinder takes a hour to heat in a 3 hour cheap period you only have 2 hours to heat house.

[Alan Ambrose]

Cooled UFH with ASHP works v well according to some friends who just discovered their HP has that function. We’ve put in some 180mm back-up ducts for central AC, but expect not to have to use them.