MVHR - comfort cool vs AC

[tanneja]

Hi all,

 

We are renovating our 3 bed 1930 semi detached (will become 4 bed).  It is as I bought it a decade ago, is a single thermostat driven central heating system.  The house is too warm in summer, cold in winter (varies by room).  Renovation will include solid floor with WFH, double/triple glazed windows, perhaps EWI, hoping with a precise builder and some air gap hunting from me we end up with a close to airtight envelope that I have the opportunity to manage. 

 

Plan is to have MVHR (BPC have recommended a Vent Axia Sentinel Kinetic FH (310m3/hr) for my 180m2 footprint (130 downstairs, 50 upstairs)) for our fresh air requirements.

 

Have read most posts remarking that, should you be building an insulated home with a decent amount of glazing, piping for an air conditioner seems sensible.  I have seen single and split units, but I can’t find much advice for where to place the internal units so they are most effective.  Would just one upstairs and one downstairs be sufficient, or really is a split unit per bedroom and living area advisable?  If a unit per bedroom is overkill (certainly expensive), are circulating ceiling fans worthwhile at night for when bedroom doors are closed, as then presumably they not getting access to the air con in the hallway.

 

I assume there will be nights when the window being open won’t necessarily bring in cool enough air for a comfortable in-room environment.  Perhaps my children may begin to suffer from tree or pollen allergies as they grow up perhaps making open windows undesirable at night.  Plus the foxes scream in the streets most nights.  I would like the flexibility to have cool rooms without opening windows if possible without substantial cost.

 

The direction I am being persuaded by a tech friend is that comfort cooling with the MVHR would at least handle the night time cooling requirement to bedrooms, does anyone think this is accurate?  If it were, I might only have to provision for AC downstairs i.e. the daytime areas.

 

Also, for any air con solution (perhaps something like this https://www.appliancesdirect.co.uk/p/iqool-3ms9k9k9k/tcl-iqool3ms9k9k9k-air-conditioner), what home climate management system do people use?  I have been recommended Honeywell EvoHome, given you can thermostat 12 rooms / locations, but don’t think it is able to manage AC for you, you would have to do that yourself manually, or perhaps something like Home Assistant IO can manage your climate heating and cooling? 

 

On the floor plans attached, please note the purple areas are vaulted, and the image of the main roof is not to scale.

 

Many thanks

JT

[SteamyTea]

There is quite a bit to unpick here.

 

If you are having underfloor heating installed, you can use that for some cooling if it is attached to a heat pump.  Just make sure that there is as much insulation under the pipework as possible.  Maybe 300mm or more.

MVHR will only allow a relatively small amount of heating/cooling with standard size ductwork.  And then you need heating/cooling elements designed into the system.  MVHR is not designed as a heating/cooling system and should not really be thought of as such.

As you intend to add extra insulation, this will also help with any overheating problems, which to be quite honest in the UK, are only a few days a year.

If the overheating is more upstairs than downstairs, adding PV to your roof may help as that converts some of the infrared radiation from the sun to electricity, approximately 15% less energy will work its way into the roof.

Positioning of cooling vents/units is really down to looks, but cold air falls, so can be fitted high up.  Noise is probably the biggest problem.  Though modern systems are quite quiet these days.

If the overheating is caused by sunlight, rather than ambient temperature, consider window blinds or reflective coating on the glazing.  You may find that it is SE and SW facing glazing that is causing the problem more than South facing (the sun is higher in the sky during the summer and this reduces the input).

 

Edited May 20, 2020 by SteamyTea

[MikeGrahamT21]

Tado is a good system for central heating controls, I have it and its always been spot on, they also have an air conditioning control too.

[tanneja]

Thanks SteamyTea,

 

The UFH was planned to be heated using our existing combi boiler, as only a year old.  Certainly plan window glass with reflective coatings on those elevations (FYI the sliding doors are facing North, to give you a feel for orientation).  The PV tip is something I didn't think of as acting as insulation, thank you, further reason to want to install.

 

Having read many posts from this forum, I'm aware home builders say comfort cooling isn't effective, I was just spooked where a consultant said it could be good for nighttime cooling (assuming you need relatively little cooling so low air flow perhaps fine).  That then fed onto thinking AC in bedrooms wasn't necessary, and so what positions would be best (for example, in the vaulted upstairs corridor as tallest place in the house (although there is a skylight that might fight the cooling), vs the downstairs living areas).  

 

Agreed that British weather usually doesn't require AC.  A month long heatwave in the summer each year could happen, I guess no one knows, but when we have had them previously,, life isn't fun here.  I would want to plan that the house could be comfortable during that time.  Presumably it is inexpensive and minimal mess to install the pipework for any AC system during the refurb, we can then live in the house and see if it is required, discovering through living in the house whether the other measures to isolate the the internal climate from the outside are sufficient.

 

I don't hate the look of the indoor units, I'm most focused on where the most effective locations would be relative to windows, room heights and function of the spaces.

 

 

Thanks MikeGrahamT21,

 

I have seen Tado online, I wondered if that would be a good alternative to EvoHome.  Do you have AC or just aware they have a module for it?  I would assume if you set the thermostat to a temperature below the outside temperature, it would engage the AC, but not otherwise?

 

Do you have thermostats throughout the house (if so a zone per room, or fewer than that)?  EvoHome seems to support 12 and is reasonably priced, so planned one thermostat per room.

 

Regards

JT

 

[MikeGrahamT21]

I've not got air conditioning at the moment, so just aware that they have a control for it.

 

It would work on the room temperature, but yes pretty sure it'll be like a normal thermostat in reverse, and only turn the AC on when required.

 

Ive got one main stat (as this does all the main work, and opentherm calculations for the boiler), and then individual radiator thermostats on each radiator to create a zone for each room. That tied in with a manifold creates a very flexible efficient heating system.

 

I was going to go with EvoHome at the begining, but it didn't have a crucial feature for me, multi-user geo fencing, not sure if they've added it yet, it could be done with EvoHome but relied on several apps to achieve it, whereas Tado has the functionality natively, as do a few others now, but Tado was the first one.

[tanneja]

Can anyone say where they would place AC units on my house design?  How many and where?  

 

Or are ceiling fans in bedrooms and living spaces the right approach?  

 

Many thanks

JT

Edited May 22, 2020 by tanneja

[SteamyTea]

4 hours ago, tanneja said:

Can anyone say where they would place AC units on my house design?  How many and where?  

 

Size is partly down to the volume of air that needs to be moved.

Location is generally in opposite corners, away from doors and windows.

 

The main problem is that air does not store much energy (1 kJ/kg.K), so to heat or cool 1 m³ of air, which has a mass of ~1.2 kg, you need to use 1.2 kJ of energy, plus the energy to move it, but that is very small in the scheme of things.

This page can be used to calculate how much power and at what flow rates are needed.

https://www.engineeringtoolbox.com/water-flow-rates-heating-systems-d_659.html

You just need to substitute the specific heat capacity of water (4.2 kJ/kg) for air (1 kJ/kg), and the density of water (1000kg/m³) for air (1.2kg/m²).