MVHR queries in relation to heating zones

[ruggers]

After delaying the start of a 2 storey masonry self build house 2 years ago, I'm looking to possibly make a start this summer and I have some questions I'd like answered to help me make decisions on where to place my heating zones, mainly linked to how the air will move. I'd prefer to understand this before I engage with the MVHR companies again as I'll be doing a lot myself.

 

Questions:

1. Are extracted rooms cooler than supply rooms when they aren't generating heat. Example, when not cooking or showering, meaning the extracted air isn't too warm from that room and it not having a supply vent?

2. We will have a large master bedroom with small ensuite, toilet, sink & small radiator only, Will it end up really cold when the ensuite radiator is off because all of the air is being removed. Knowing this will let me decide if I have the ensuite as part of the same zone as the master bedroom or do I have it on open circuit (Heats when any upstairs radiator is called).

3. Hallway & landing I was told, they will unlikely need vents as the air will move between them from other rooms. If so, will there be cold spots in these areas with air movement? I'm trying to decide if I have the hallway on its own temperature zone, link it to another zone, or have it on an open circuit to keep the central temperature balanced with it being a central hallway.

 

Details: The house design is fairly basic, ground and first floor, cold loft, central hallway and landing. Previous talks with companies were showing (5) supply air vents to 4 bedrooms & the downstairs living room. Extracts (6 Vents), from the ground floor kitchen, utility room, downstairs bathroom, plant room, upstairs bathroom and ensuite. We will have wet UFH downstairs zoned, & radiators upstairs some zoned.

 

 

[joth]

37 minutes ago, ruggers said:

Are extracted rooms cooler than supply rooms when they aren't generating heat. Example, when not cooking or showering, meaning the extracted air isn't too warm from that room and it not having a supply vent?

No, it's the opposite.

Assumption 1: this question is in regards to heating season, when the outside air temperature is (much) lower than the internal temperature.

Assumption 2: the building is to a high spec for insulation and airtightness

 

An MVHR supply vent puts out air slightly colder air than the internal average air temperature. So in a steady state, and ignoring highly localised sources of heating, supply side rooms will be slightly colder than the average internal temperature, and thus extract rooms sightly warmer.

Now most designs naturally arrange heating sources to compensate for this, focusing emitters in the living areas which tend to be supply side rooms. But also those rooms tend to have more glazing which further cools them. So we'd need all those details to give any sort of real estimate.

 

Does that make sense? Hopefully that helps with the other questions

Edited February 20, 2022 by joth

[JohnMo]

Comments as above plus

Basics.

MVHR, does not move heat about very effectively.

 

Remember you will only be moving 0.3 to 0.5 air volumes an hour.

 

Air will flow through rooms with a supply and then into and across a room with an extract.  So all rooms are having air exchanged.

 

Having an en-suite part of the bedroom loop isn't a good idea as the temperature requirements are very different.  Ensuite warm, bedroom cool.

 

I would look at the MVHR in its own right and the heating in own right.  You have to extract in wet rooms and supply in dry rooms.

 

If you are very well insulated, having loads of zones isn't a real benefit, as the heat loads are so low.  We have bedrooms that can shut off heat, but cannot call for heat.  Everything else is s single zone.  We have electric towel rads in bathrooms and en-suites.

[ruggers]

13 minutes ago, joth said:

Now most designs naturally arrange heating sources to compensate for this, focusing emitters in the living areas which tend to be supply side rooms

Both assumptions are correct, and it will be airtight and highly insulated as per regs, but I should maybe rephrase part of Q2.

 

I understand that the incoming air will be lower temperature than what is being extracted due to the heat exchange process/loss. But If i have a small ensuite that is enclosed, with an MVHR extract vent, if the only source of heat in that room is a radiator, during the winter months, when that radiator isn't turned on because the zone it's linked to isn't calling for heat, would it not end up really cold because any air that's in that room has been extracted out? If I had no extract in there, then all of that heat would be retained in the ensuite room after the radiator turns off if I insulate the walls around it correctly. Although any smells wouldn't escape with no extract.

 

I don't quite understand the quoted line?

[JohnMo]

If you don't extract you would also end up with lots of damp issues also.

 

Yes it would end up cool.  So don't link to an are area that wouldn't be calling for heat.  We have electric rads in ensuite and bathroom for that reason.

 

You say you are well insulated per regs.  Do you mean you have building regs insulation only?

 

 

[ProDave]

How well insulated are you planning to make the house?

 

Many of us find in a house that in insulated to near passive house standards and properly air tight, there is no such thing as cold rooms anywhere, and many of us have no heating upstairs because it is simply not needed.  We have UFH in the en-suite and main bathroom, not because the rooms needed any heating but "someone" wanted warm tiles to walk in in the morning.

[ruggers]

@ProDave Thats sounds really good managing to not require them upstairs. The site is about 400ft above sea level and can get a bit chilly in Winter, I'm not sure what to expect in terms of heat loss from a masonry build with cold loft compared to some timber frames. I'll be having 100mm PIR in the cavity, rockwool in all of the stud walls and between the ceiling & floors. Loft insulation between and over the ceiling chords, I was going to enquire about the foil quilt for under the rafters more as a heat deflector in summer to stop the slates transferring so much heat into the loft but the loft is trussed so quite awkward to make it sealed. There may be no purpose to the superfoil type if it's not sealed. I was considering adding insulated plasterboard certainly to the North facing walls, but unsure if I do all rooms in it or not until I 2022 quotes.

 

@JohnMo

1 hour ago, JohnMo said:

 We have bedrooms that can shut off heat, but cannot call for heat.  Everything else is s single zone.  We have electric towel rads in bathrooms and en-suites.

If you can shut off the heat but can't call for it, is this just by using standard TRV's? What's the benefit to having electric towel rails over water heated?

 

58 minutes ago, JohnMo said:

Yes it would end up cool.  So don't link to an are area that wouldn't be calling for heat. 

What are you referring to as linking to an area, do you mean don't extract from the ensuite, or do you mean to make sure the ensuite radiator is always linked to an area that will be calling for heat throughout the day?

 

I've various reasons for wanting zones, some might not need applied to a new build vs my old current house with only partial insulation. 1.Temperature control over certain rooms, like living room at night when people are in bed not wanting bedrooms heated. 2. When working from home just heating the room i'm in for 8 hrs or heating only 2 rooms early morning as I leave for work 2.5 hrs before the kids. 3. I just thought it was more efficient to only heat the rooms we use the most on some days. I'm used to an older house with a living room fire and all radiators controlled from one thermostat. It heats up well and loses it well in the old part with no wall insu., new extensions better.

[JohnMo]

General comments, if you are really well insulated, 0.15. U value or better and airtight, your heating demands are very low, so the heat loss is slow.  I have my heating set for 19 degs, 24/7, the boiler comes on once a day to keep that temperature.   My average heat input by gas has been 2.2kW since September for 190m2 single storey.

 

"If you can shut off the heat but can't call for it, is this just by using standard TRV's? What's the benefit to having electric towel rails over water heated."

 

Answer, we have UFH in the bedrooms, but like cool bedrooms, when the house is warm in the winter, we can open the bedroom door and within an hour the room is the same temperature as the rest of the house.  But with doors closed we can have the bedrooms a few degrees cooler.  We just wanted to be able to switch the UFH of in the bedrooms sooner than the rest of the house.  We are using a standard Salus head on the UFH manifold.

 

We have electric towel rails for two reasons. First is for summer towel drying, so there is no requirement to use the CH.  Second our house is super insulated and the UFH only needs to come once per day, the electrical towel rail allows flexibility for towel drying in winter also.

 

"What are you referring to as linking to an area, do you mean don't extract from the ensuite, or do you mean to make sure the ensuite radiator is always linked to an area that will be calling for heat throughout the day?"

 

Answer, I am talking about the heating not ventilation.  Have the ensuite/bathroom radiators on their own zone for heating. One of the reasons for electric towel rails, so I heat these rooms even with the rest of the heating off.  If I was doing it again I would have electric UFH instead of water, for complete flexibility.

[ruggers]

What type of build construction and airtightness do you have to achieve them levels, it must be well insulated in the walls floor and roof area. Do you just have the 1 thermostat then?

 

I understand the benefit of the electric towel rails now but I wouldn't like an all electric house with it costing 4 x more per KW hr, It can be more efficient in response times but electric UFH seems poor and expensive to run.

[JohnMo]

Construction

Floor, 200mm, reinforced concrete, 200mm PIR, 100mm concrete floor with UFH in all rooms.

 

Walls Durisol, with cement, lime parge coat, service battons and plasterboard.

 

Roof all vaulted ceilings, with 300 to 350mm spray foam insulation. Aluminium foil vapour control, airtightness layer on ceiling, draping down 200mm on to wall and glued to wall, service battons and plasterboard.  Floor to wall perimeter at dpc, airtightness paint.

 

Triple glazed windows.

 

One thermostat in the hall.

 

Gas combi boiler, but thermal store as buffer for central heating, and pre heat for DHW and solar PV immersion diverter.