Alternative to AC - Might be useful going forwards

anon_ymous

I've seen this 

https://www.greensquare.co.uk/blog/2020/8/19/air-conditioning-how-cooling-your-home-can-be-from-clean-renewable-energy-too

And that does seek pretty decent as a way to not only heat your house but to then also recover that same heat, for use later on. I'm sure they're not the only company doing that too 

Reed_Richards

It all seems to be highly ambiguous.  They mention using an ASHP to cool you home and this is perfectly feasible.  But using radiators for cooling is not very effective and condensation can be an issue.  And an ASHP used for cooling requires planning permission whereas one used purely for heating is usually classed as a permitted development.

Then without pausing for breath they switch to claiming that they can use a Mechanical Ventilation with Heat Recovery system to cool your home.  The point of such systems is to ventilate your house without causing it to lose heat.  "Heat Recovery" in the name is the clue to this.  This cannot cool your home significantly if it is working as intended and it absolutely cannot cool your home if it is hotter outside than inside.   

QrizB

Reed_Richards said:

It all seems to be highly ambiguous.

I'd go so far as to say misleading.

They mention using an ASHP to cool you home and this is perfectly feasible.

They seem to be saying "AC = bad, ASHP = good" but they're fundamentally the same thing. Many of the devices sold in the UK as ASHPs are rated to provide either heated or chilled water, but the chilled function is not used in a system that uses radiators or UFH.

(They do say they'll use fan coils rather than rads or UFH for an ASHP cooling system; you can use fan coils for heating, too.)

Then without pausing for breath they switch to claiming that they can use a Mechanical Ventilation with Heat Recovery system to cool your home. ...  This cannot cool your home significantly if it is working as intended and it absolutely cannot cool your home if it is hotter outside than inside.   

I think they're saying that once you have cooled your house, MVHR will help to keep it cool. And I think they're probably right on that count. But it's part of a system, not a solution in itself.

Reed_Richards

QrizB said:

I think they're saying that once you have cooled your house, MVHR will help to keep it cool. And I think they're probably right on that count. But it's part of a system, not a solution in itself.

MVHR does not have a cooling function so can only help keep your house cool by stopping you opening windows.  What it can do is to reduce the moisture content of the cooled air inside your house by exchanging it for dryer external air.

QrizB

Reed_Richards said:

QrizB said:

I think they're saying that once you have cooled your house, MVHR will help to keep it cool. And I think they're probably right on that count. But it's part of a system, not a solution in itself.

MVHR does not have a cooling function so can only help keep your house cool by stopping you opening windows.  What it can do is to reduce the moisture content of the cooled air inside your house by exchanging it for dryer external air.

I don't think that's true.

MVHR includes a passive heat exchanger, and heat (like water) only flows downhill. In cold weather it will transfer heat from your warm exhaust air into your cold make-up air, so the make-up air is warmer and the exhaust air colder. In hot weather it should transfer heat from your warm make-up air into your cold exhaust air, so the make-up air is cooler and the exhaust air warmer.

Screwdriva

We can run two aircons solely on our rooftop solar for 6 hours a day easily. Again, misleading. 

Meatballs

Reed_Richards said:

QrizB said:

I think they're saying that once you have cooled your house, MVHR will help to keep it cool. And I think they're probably right on that count. But it's part of a system, not a solution in itself.

MVHR does not have a cooling function so can only help keep your house cool by stopping you opening windows.  What it can do is to reduce the moisture content of the cooled air inside your house by exchanging it for dryer external air.

I think some MVHR models will take cooling input from ASHP to help chill the output - but it's only a small chilling effect for the house overall.

https://www.zehnder.co.uk/blogarticles/keeping-it-cool-combining-ventilation-active-cooling-combat-overheating

Reed_Richards

QrizB said:
i don't think that's true.

MVHR includes a passive heat exchanger, and heat (like water) only flows downhill. In cold weather it will transfer heat from your warm exhaust air into your cold make-up air, so the make-up air is warmer and the exhaust air colder. In hot weather it should transfer heat from your warm make-up air into your cold exhaust air, so the make-up air is cooler and the exhaust air warmer.

So in cold weather the heat exchanger ensures that the make-up air is only a little bit cooler than the exhaust air so you get fresh air at the expense of only a little bit of cooling.  In hot weather the heat exchanger ensures that the make-up air is only a little bit warmer than the exhaust air so you get fresh air at the expense of only a little bit of heating.  Nonetheless in hot weather (i.e. hotter outside than in) what you get from your MVHR is a little bit of heating but a lot of fresh air.

Now potentially you could add active heating or cooling to a MVHR system (as per @Meatballs link) but that ought to have a different name to avoid confusion.     

QrizB

Reed_Richards said:

QrizB said:
i don't think that's true.

MVHR includes a passive heat exchanger, and heat (like water) only flows downhill. In cold weather it will transfer heat from your warm exhaust air into your cold make-up air, so the make-up air is warmer and the exhaust air colder. In hot weather it should transfer heat from your warm make-up air into your cold exhaust air, so the make-up air is cooler and the exhaust air warmer.

So in cold weather the heat exchanger ensures that the make-up air is only a little bit cooler than the exhaust air so you get fresh air at the expense of only a little bit of cooling.  In hot weather the heat exchanger ensures that the make-up air is only a little bit warmer than the exhaust air so you get fresh air at the expense of only a little bit of heating.  Nonetheless in hot weather (i.e. hotter outside than in) what you get from your MVHR is a little bit of heating but a lot of fresh air.

Yes, exactly that. It should reduce the A/C demand (by comparison to other ventilation options) but it won't in itself make you cooler.

70sbudgie

What sort of efficiency does a MVHR run at? Would the two in combination reduce the energy required for heating / cooling?  Over the last couple days, the thing I have really noticed is the apparent lack of air! Opening windows that normally create a breeze was a mistake.

QrizB

70sbudgie said:

What sort of efficiency does a MVHR run at? Would the two in combination reduce the energy required for heating / cooling?  Over the last couple days, the thing I have really noticed is the apparent lack of air! Opening windows that normally create a breeze was a mistake.

Here's a blog post from a major manufacturer (so they have a vested interest) that discusses some of this:
https://www.xpelair.co.uk/what-is-mvhr