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I will soon be building a well insulated air tight contemporary house, which will have an MVHR system. We have south facing glazing, so I am aware of solar gain etc. In the winter, we will be able to heat the house with very little cost, using the thermal mass to store heat, and the MVHR system will keep the air fresh and circulated. However, I am thinking about hot weather when we might want to cool certain areas of the house (e.g. in basement where it is not possible to open windows to cool the room), so I was thinking of an AC system like Invisible.AC (https://www.invisible.ac/). Does anybody have any experience of using this system and/or any other way to cool the house as well as keep the air clean ?

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Posted (edited)

There are lots of suggestions made here regularly.

 

eg

 

Have a facility in your ufh to circulate heat around the slab ie unheated water. Here you might circulate it between Basement and GND.

 

For a basement I would look at using light wells as cooling wells, ie opening high level windows to cool the basement using the stack effect.

 

You need to manage your insulation such that the heat pulse coming in is reversed overnight, with appropriate characteristics to make that more-or-less happen.

 

Wildcard: if your wall is tanked, does it help to have a pond on the other side? To me this feels like too much effort for the potential benefit.Lutyens_houses_and_gardens_(1921)_(14577

 

Ferdinand

Edited by Ferdinand

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over heating basement ?

not convinced  there would be a problem in basement

that's why wine cellars are in  the basement -the ground around it keeps temp much more stable and you could always insulate under side of floor above to keep heat from radiating downwards 

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@Bitpipe has an insulated basement and I'm sure his experience is that it doesn't overheat.

 

I use our ASHP in reverse mode to cool the (insulated) slab on the ground floor. We have concrete floors so this is very effective. It's a far more natural "coolth" than that provided by aircon (I spent a lot of time in Australia when I was growing up, so I'm very familiar with aircon!) 

 

I'm convinced that this helps keep the upstairs rooms slightly cooler too.

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1 hour ago, jack said:

@Bitpipe has an insulated basement and I'm sure his experience is that it doesn't overheat.

 

I use our ASHP in reverse mode to cool the (insulated) slab on the ground floor. We have concrete floors so this is very effective. It's a far more natural "coolth" than that provided by aircon (I spent a lot of time in Australia when I was growing up, so I'm very familiar with aircon!) 

 

I'm convinced that this helps keep the upstairs rooms slightly cooler too.

Sounds interesting. How does the heat pump cool the slab ? Are you pushing cold water around the UFH pipes ?

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1 hour ago, scottishjohn said:

over heating basement ?

not convinced  there would be a problem in basement

that's why wine cellars are in  the basement -the ground around it keeps temp much more stable and you could always insulate under side of floor above to keep heat from radiating downwards 

Good point about wine cellars. Thank you.

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31 minutes ago, Tim Alsop said:

Sounds interesting. How does the heat pump cool the slab ? Are you pushing cold water around the UFH pipes ?

 

Yes, exactly that. 

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A wine cellar in an old building isn't equivalent to a cellar in a modern, well insulated building.

 

An old wine cellar will be thermally connected to the surrounding earth and have no significant internal heat input, so will maintain a temperature roughly the same as the underground temperature, a few degrees C.

 

A modern basement should have a large amount of insulation isolating it from the moderating effects of the surrounding earth. It is also likely to have significant local heat input, depending on its use. Might have a plant room or be used as a home theatre or a gym etc, all of which will generate heat and introduce the possibility of over heating.

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2 hours ago, jack said:

@Bitpipe has an insulated basement and I'm sure his experience is that it doesn't overheat.

45 minutes ago, billt said:

A modern basement should have a large amount of insulation isolating it from the moderating effects of the surrounding earth. It is also likely to have significant local heat input, depending on its use. Might have a plant room or be used as a home theatre or a gym etc, all of which will generate heat and introduce the possibility of over heating.

 

 

We have 300mm EPS 200 under the 300mm slab and 200mm EPS 70 on the outside walls of basement. It's about 115m2 divided into four rooms and the plant room, each of the back to back rooms open into each other.  

 

There's a plant room with UVC, gas boiler and MVHR unit. Two TV rooms with gaming consoles etc and a room with lots of boxes and a freecycled running machine that I optimistically call the gym :)

 

Always the same temp year round, about 22. Feels warm in winter and cool in summer. No heating down there, MVHR for ventilation.

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4 hours ago, billt said:

A wine cellar in an old building isn't equivalent to a cellar in a modern, well insulated building.

 

An old wine cellar will be thermally connected to the surrounding earth and have no significant internal heat input, so will maintain a temperature roughly the same as the underground temperature, a few degrees C.

 

A modern basement should have a large amount of insulation isolating it from the moderating effects of the surrounding earth. It is also likely to have significant local heat input, depending on its use. Might have a plant room or be used as a home theatre or a gym etc, all of which will generate heat and introduce the possibility of over heating.

yes, I will have a plant room and cinema room and these are other reasons why I want to find a cooling solution. Thank you

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3 hours ago, Bitpipe said:

 

We have 300mm EPS 200 under the 300mm slab and 200mm EPS 70 on the outside walls of basement. It's about 115m2 divided into four rooms and the plant room, each of the back to back rooms open into each other.  

 

There's a plant room with UVC, gas boiler and MVHR unit. Two TV rooms with gaming consoles etc and a room with lots of boxes and a freecycled running machine that I optimistically call the gym :)

 

Always the same temp year round, about 22. Feels warm in winter and cool in summer. No heating down there, MVHR for ventilation.

Thats good to hear. Thank you. 

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19 hours ago, Tim Alsop said:

Thats good to hear. Thank you. 

 

I did consider UFH pipe in the basement floor and engineering some kind of heat dump outside the insulated envelope of the basement but dropped the idea due to cost.

 

You could consider chilling the MVHR fresh air in summer, although the volume of air moved is small so the effect would be slight. 

 

Remember that the biggest contributor to overheating is usually solar gain - our basement light wells are quite deep so rarely get direct sunlight, its more diffuse.

 

The only change I'd make is to have one of the high level windows openable (in the room diagonally opposite  the room that has the exit & stairs to ground level) - this way I could create some cross draft for additional purging of warm and stale air - the MVHR does he job eventually.

 

If you're really concerned about overheating, make provision for  a split air con (i.e. ducting etc) in the basement and you can install it later if the problem arises. If not you can just plug the ducting.

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20 minutes ago, Bitpipe said:

If you're really concerned about overheating, make provision for  a split air con (i.e. ducting etc) in the basement and you can install it later if the problem arises. If not you can just plug the ducting.

Thats a good idea - ducting will be cheap compared to the air con unit, so I will explore this option for peace of mind.

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12 minutes ago, Tim Alsop said:

Thats a good idea - ducting will be cheap compared to the air con unit, so I will explore this option for peace of mind.

 

One of the home build rules of thumb is to make provision for things you're not 100% sure you'll need but will a pain to retrofit later, or just for peace of mind.

 

By way of example, before we laid the driveway in Jan 2018 we ran ducting under the entrances to facilitate driveway lighting at a later date (as it's resin bound stone, I never want to have to cut into it.)

 

Then when commissioning the power to the garage we realised that the SWA between garage and kiosk had been damaged at some point in the driveway construction so we were able to pull a new run using the existing duct.

 

Ducting is your friend :)

 

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2 hours ago, Bitpipe said:

 

One of the home build rules of thumb is to make provision for things you're not 100% sure you'll need but will a pain to retrofit later, or just for peace of mind.

 

By way of example, before we laid the driveway in Jan 2018 we ran ducting under the entrances to facilitate driveway lighting at a later date (as it's resin bound stone, I never want to have to cut into it.)

 

Then when commissioning the power to the garage we realised that the SWA between garage and kiosk had been damaged at some point in the driveway construction so we were able to pull a new run using the existing duct.

 

Ducting is your friend :)

 

 

 

Very true, and I dearly wish that I'd thought to add a duct behind our bathroom ceiling so that I could fit an air-to-air unit right up near the top of our entrance hall.  Being a tall (>6m high) space, with glazing on the South facing gable, this is the part of the house that gets the most solar gain, and being able to cool the air right at the top would be useful.  I've been thinking of ways to try and get a duct, big enough to take the pipes from a split air-to-air unit, up behind the ceiling, which isn't easy as the service space 50 x 50 battens run at right angles to the direction I'd like to run the duct.

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In my proposal on MVHR a duct cooler has been specified - well it is sold as a heater :

https://www.bpcventilation.com/hot-water-duct-heater-range?gclid=CjwKCAjwndvlBRANEiwABrR32AYX25XU3baX6tcuGKne9hKegBRxmoPRO44n3Nje7XIHpUcwrr1PjRoCLCAQAvD_BwE

 

though presumably will heat or cool depending on the liquid temp you run through it.

 

BPC are working on the design at the moment but hopefully I can run this with a circuit from the ASHP but given the low flow rates this probably means insulating most of the out-flows to avoid temp losses en-route. Don't think I'd want this to be used for heating so would need to build that logic in somehow.

 

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If using a hydronic duct heater as a cooler then it will have to have a condensation catchment tray fitted and a condensate drain, as duct heaters don't have this.  It will also need to be made of corrosion resistant materials, as it will be damp whenever it's cooling.

 

I've been working on converting a hydronic duct heater into a cooler, to add to our system, but have run into a couple of snags with getting a condensate catchment and drain system to work OK.  Not insurmountable, but it has meant making a completely new housing, as there was no easy way to adapt the duct heater housing that I could see (mainly because if I'd tried to it would have presented corrosion problems).  I only tried to adapt a hydronic duct heater because they are half the price of duct coolers...

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Yes - interesting, when I spoke with them they did mention the condensate drain but the spec sheet they sent does not match that 🙂 Will see what ends up in the design. The spec sheet has VentMatika as the brand for the duct heater/cooler. Will update when I know more.

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Posted (edited)

I am now considering the use of a ground-air (or ground-brine) heat exchanger to cool the air on hot day before input to MVHR. It is not same as air conditioning because of air flow rate, but it might be good enough to help regulate temp in house on a hot day. Has anybody else used this kind of product ? Example can be found at https://www.rehau.com/gb-en/building-technology/renewable-energy/ground-air-heat-exchangers

Edited by Tim Alsop

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2 minutes ago, Tim Alsop said:

I am now considering the use of a ground-air (or ground-brine) heat exchanger to cool the air on hot day before input to MVHR. It is not same as air conditioning because of air flow rate, but it might be good enough to help regulate temp in house on a hot day. Has anybody else used this kind of product ? Example can be found at https://www.rehau.com/gb-en/building-technology/renewable-energy/ground-air-heat-exchangers

 

These have a fairly interesting reputation, so very well worth looking carefully to be absolutely 100% certain that the company providing the system and undertaking the installation know exactly how to make the system safe.

 

This is an example of what may happen if the installation goes wrong: https://www.greenbuildingadvisor.com/article/belgian-passivhaus-is-rendered-uninhabitable-by-bad-indoor-air

 

There's also an earlier thread on MVHR cooling here:

 

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