MVHR with active cooling and/or AC in a flat

[JamesFR]

Hi All,

I am writing to see if there is a good way to add cooling to an existing MVHR system. I have read quite a few topics from this forum on this, but they don't exactly seem to answer the question, mostly because I live in a flat where a split system is not feasible:

 

• This thread has the most information concludes that an ASHP seems to be the best option, which is not possible.
• This thread hints that comfort cool is ineffective.
• This thread stops quite inconclusively and is quite focused on a house.
• Here is a discussion about summer bypass, but unfortunately the unit that came with my flat seems to be the cheapest and does NOT have a summer bypass (MRXBOX95-WM2)
• This thread went off the rails a bit but has some ideas.

 

The flat has huge windows on both aspects. I have done what I can to reduce heat gain with reflective film on part of the windows and big curtains, but outside shades are not an option. The flat is very well insulated and is on the 4th floor, leading it to get quite warm at night even without hot weather. For example, I aired it out yesterday and went to bed with it being 22C, but woke up with it at 25C despite the outside temperature being 12C. I suspect the cheap MVHR is part of this, but the bathroom does not have windows so I don't have much choice but to keep it on all the time. I can't seem to get it off boost mode either. Why not just open the windows at night? Unfortunately, it is quite close to a very active train line, and I find it difficult to sleep with loud trains going by constantly.

 

As far as I can tell, these are my options:

• Portable A/C
  • Pros: Cheap
  • Cons: Loud, ugly, inefficient especially because windows are only inward opening, have to open window
• Get water cooled A/C installed
  • Pros: Effective
  • Cons: Very expensive to have done, loss of most storage space in the flat, increased water bill (??)
• Adiabatic cooling on MVHR, such as https://www.ventilationland.co.uk/en_GB/p/homevap-mvrh-cooler/9745/#pdpBlogs
  • Pros: Goes onto existing system, cheaper than water cooled A/C
  • Cons: Very little info on effectiveness (could work moderately? not enough airflow?), unclear if there are many who install these
• MVHR system with cooling, such as https://www.nuaire.co.uk/product-list-page/mrxbox-hybrid-cooling-system
  • Pros: Same ductwork
  • Cons: Can't find any reviews on effectiveness or cost

 

I know this forum is more focused on homes, but I would appreciate any thoughts any knowledgeable folks might have.

 

 

[JohnMo]

Simple facts are

MVHR airflow rates are way to low to have much or any effects on room temperature. You are only exchanging the air once every two the three hours. 

44 minutes ago, JamesFR said:

Adiabatic cooling

Read above, plus that form of cooling works by adding water vapour to the air to cool it down and play with dew points etc. but in the UK generally the humidity in the summer is high so effectively, it's not much use.

 

Water based Aircon is a waste of good water unless you can recycle the water via buffer or something.

 

If you can't do a split Aircon or traditional heat pump, I would look at through wall Aircon. Basically two duct holes in the wall and everything sits in the room like a radiator.

Not a recommendation just the first site I came to

https://www.nationalheatershops.co.uk/c/ptacs/

[JamesFR]

Thanks so much for your reply.

5 minutes ago, JohnMo said:

Read above, plus that form of cooling works by adding water vapour to the air to cool it down and play with dew points etc. but in the UK generally the humidity in the summer is high so effectively, it's not much use.

This makes sense to me, but what doesn't make sense is that the maker of this unit is a Dutch company (HomEvap). Isn't it just as humid there? Are all these products this company sells just a scam?

 

6 minutes ago, JohnMo said:

If you can't do a split Aircon or traditional heat pump, I would look at through wall Aircon. Basically two duct holes in the wall and everything sits in the room like a radiator.

I like this idea a lot, but I have a difficult time believing I can get permission from the freeholder.

[JohnMo]

1 hour ago, JamesFR said:

permission from the freeholder

Don't ask?

[JamesFR]

13 minutes ago, JohnMo said:

Don't ask?

HA

Is this really something people do? I think I'd be too nervous it would be a major hang up if I wanted to sell up. Plus, surely someone would notice me drilling a hole in the side of a medium-rise block.

[NailBiter]

2 hours ago, JohnMo said:

Water based Aircon is a waste of good water unless you can recycle the water via buffer or something.

I'm well out of my comfort zone so I might be chatting bollocks but presumably a hydronically linked AC system like the Panasonic M Series with blowers would be an acceptable solution and not a waste of good water?

[JohnMo]

54 minutes ago, NailBiter said:

I'm well out of my comfort zone so I might be chatting bollocks but presumably a hydronically linked AC system like the Panasonic M Series with blowers would be an acceptable solution and not a waste of good water?

Different system, the one the OP is referring to takes tap water through an indoor heat pump unit (W2W or water to refrigerant) and then said water is routed to drains never to be seen again. Many (100s) m3 of water goes to drains system over a summer period even when there is a hose pipe ban in force.

[JamesFR]

13 minutes ago, JohnMo said:

Different system

Unfortunately this is correct, the water systems are like these: https://www.coolyoudirect.co.uk/apartment-air-conditioning-systems/.

Notice they never say the running costs or water usage.

[NailBiter]

1 hour ago, JamesFR said:

Unfortunately this is correct, the water systems are like these: https://www.coolyoudirect.co.uk/apartment-air-conditioning-systems/.

Notice they never say the running costs or water usage.

 

Probably best avoided, both for your pocket and the planet.

 

Can you give us some more info, e.g. rough floor plan (simple sketch is fine) and where the MVHR is etc? Total area to cool would be a useful metric too.

I'm wondering if you can't take an input for an AC / Heat pump from the same place the MVHR does and exhaust to the same place it does (to avoid holes in the wall). You can then hydronically link the main unit to any blowers you need just like running radiator pipe but for cooling. 

 

 

Edited May 16 by NailBiter

[JamesFR]

28 minutes ago, NailBiter said:

simple sketch is fine

Green is the cupboard where the MVHR is, red are extracts and blue are vents. The hoses in/out of the MVHR are flex PVC into the ceiling, then hard rectangle PVC. Total area is about 70m2.

 

The idea is interesting, but I've read that the ducting has to be larger for AC than for MVHR.

[JohnMo]

You could explore this

 

https://coolenergyshop.com/collections/air-source-heat-pumps/products/activair-3kw-indoor-air-source-heat-pump

 

Tee it into you MVHR pipes that go outside, you would have to take a proper look to see if it works. There are no noise figures so that would need to be understood and it's a little vague on cooling, it seems to have an icon but no other mention. Then connect to a fan coil radiator.

[Mike]

13 hours ago, JamesFR said:

Adiabatic cooling on MVHR, such as https://www.ventilationland.co.uk/en_GB/p/homevap-mvrh-cooler/9745/#pdpBlogs

• Pros: Goes onto existing system, cheaper than water cooled A/C
• Cons: Very little info on effectiveness (could work moderately? not enough airflow?), unclear if there are many who install these

I've just installed one in my French apartment renovation as I had no other viable options. However the chances are the summer may be over before it will be operational, so unlikely to be able to provide feedback soon (and France isn't the UK). There are a few useful reviews on the Netherlands version of the Ventilationland website that you can put through a translator.

 

From my research, in theory such units should be able to drop the air temperature to within 3 or 4° of the wet bulb temperature. According to the 2005 ASHRAE Handbook, in London the monthly design dry bulb and mean coincident wet bulb temperatures for July are 30.9° and 19.7°, so nominally you may be able to drop the temperature (in the duct) to around 23 or 24°C (3 or 4° above 19.7°), which would be a useful improvement over pulling in air at 31°.

 

However the airflow rate is a limiting factor. In my case I have plenty of spare capacity to boost the flow rate in heatwave conditions to well over 1 air changes / hour, which will help. If your unit is low end, maybe that's not an option.

 

While not huge, the HomEvap does require a bit of space - it has 200mm duct connections, needs enough clearance to rotate it to change the cartridge (unless you have top access), and needs a drain connection. And it must be horizontal.

 

Edited May 16 by Mike

[JamesFR]

11 hours ago, Mike said:

few useful reviews

Thanks for this. Combined with this, @JohnMo's comments, and the low ACH (which I'm not sure I've calculated correctly) from the cheap MRXBOX, I think this option is a no.

[NailBiter]

I think maybe there are two figures here:

 

1. How much air you can push through the intake / exhaust vents without creating too much noise.

 

2. How much your current MVHR pushes through them.

It might be a different value.

[Mike]

7 hours ago, NailBiter said:

1. How much air you can push through the intake / exhaust vents without creating too much noise.

 

2. How much your current MVHR pushes through them.

 

And, if there are no other viable means of cooling, 'too much noise' may be somewhat elastic. Normally the in-room diffusers should run whisper-quiet but, in a heatwave, given a choice between being unable to sleep due to too much noise -vs- too much heat, the tolerance for noise may well increase.

[JamesFR]

9 hours ago, NailBiter said:

It might be a different value.

 

2 hours ago, Mike said:

tolerance for noise may well increase.

I think these are good points. I think I currently have a pretty high tolerance for noise relative to the train outside the window at night.

But I think the issue for me is that without a specific product in mind and a ready installer I probably can't do it. I acknowledge I'm probably on the wrong forum given this. I just do not see any examples of any splicing their MVHR with an internal ASHP or air conditioner.

[NailBiter]

I'm no plumber so again massive pinch of salt here but it might matter how you connect the vents together. You don't want two exhausts blowing air at each other, you want them both joining together smoothly and pushing the air to outside. Think sanitary T waste pipe fitting vs a straight T.

[SteamyTea]

On 16/05/2024 at 09:16, JohnMo said:

I would look at through wall Aircon. Basically two duct holes in the wall and everything sits in the room like a radiator

May have to get permission and a SE involved when drilling through a tower of flats.

I am still thinking of getting one to heat my place.

[JamesFR]

On 19/05/2024 at 17:51, SteamyTea said:

permission

@SteamyTea You think you might get permission? Or are you just commenting that it would be needed for flats generally?

[SteamyTea]

7 hours ago, JamesFR said:

Or are you just commenting that it would be needed for flats generally

That bit.