HRV: Cool Air in Summer - A Myth?

Quack13

I have noticed some suppliers of HRV selling their product as supplying 'Warm air in Winter, cool air in Summer'.

I have also come across a reputable HRV supplier saying that HRV does NOT supply Cool air in the summer and HRV is not built for this. It's just a case of turning it off on a very hot summer's day and opening the windows.

Would be interested to hear what people think about this.

Does anyone use HRV to cool the house inte summer or is this not possible?

Q

Juantorena

I stand to be corrected on this but.....

As I understand it the only way a MHRV system can positively cool distributed air in the house is if it has external ducting - usually underground - which feeds into the intake air ducting and then bypassing the heat exchanger in the unit. During warm weather the ground will be slightly colder than the outside air therefore the incoming air will be 'cooler' than if it was taken directly from outside.

If you know what I mean!

gman2k

What people are talking about is a summer bypass setting, where the unit continues to pump in fresh air, but does not utilize the heat exchanger.
Therefore, if your house is building up heat during the summer due to passive solar gain (large southern windows) you let the unit 'suck' this heated air from the house and replace it with cooler air from the outside.
As I'm still in the building process, this will be important to me when we are finally in the house, as last week at 9.30am it was 29deg in the house (MHRV is not functioning yet.)

What you don't want to do is not use the system during the warmer months, and have to open windows for ventilation - therefore introducing more dust/ pollens etc into the house.

@OP, I'm surprised that the supplier you talked to suggested you turn off the system and open windows! His system must not include a summer bypass option! He is right in the fact that the air will not be cool (like air conditioning) but it will be the external ambient air temperature.

Also, @ Juantorena, your underground ducting would not cool down the air temperature much, as it is only briefly passing underground.
More importantly, I believe that it is best for the intake to be on the northern side of the house, so as the air temperature here may be lower, if the intake is not getting direct sunlight.

Quack13

Here is text from the FAQ on the HRV suppliers site:

---

The system does not have a summer bypass. What can I do to keep the house cool in summer?

A HRV system is not a cooling system and can never be, despite what some suppliers might claim. A thermostat can be fitted to turn off the supply fan in summer, thereby giving an energy saving and leaving you with an extract system to deal with moisture. At this time of the year, thermal efficiency will not be an issue and windows can be opened.

---

This is a very reputable HRV supplier btw.
One of the most well respected in the country I would say.

CJhaughey

This is true, HRV doesn't do cooling.
It just supplies air, warmed in winter or ambient in summer.

If you want cool air fit an ASHP and run it on the reverse setting.
Not as efficient but it still makes a big difference in indoor temps.

Cheeble

I'd say the supplier is being pretty straight with you, and offering a good option.

Why go for a technology based solution? Go on, just open the window, you might like it . And if that's not sufficient, create some natural ventilation columns in the house that will extract through updraught convection.

Either of these options will be maintenance-free and have zero running costs. Why choose anything else?

Cheeble-eers

CJhaughey

Cheeble wrote: »

I'd say the supplier is being pretty straight with you, and offering a good option.

Why go for a technology based solution? Go on, just open the window, you might like it . And if that's not sufficient, create some natural ventilation columns in the house that will extract through updraught convection.

Either of these options will be maintenance-free and have zero running costs. Why choose anything else?

Why choose anything else?
For a start you might suffer from an allergy to pollen, very common these days.
Your open windows and updraft will no doubt bring large amounts of pollen in to the house.
Good quality HRV systems that are well maintained have filters that will remove most allergens and dust before they enter the house.
You also get a lot of flies in summer, not having to open windows will reduce the incidence of these in your house, they can still come in via doors but the chances of flies, bees and wasps entering are reduced.

How do you ventilate at night? Not all areas are secure or crimefree enough to have windows open at night.

What happen to the updraught convection columns in winter? do they still let all the warm air out and suck in cold air?
If you do block them up to stop heat loss how do you ventilate the house?

Cheeble

For a start you might suffer from an allergy to pollen, very common these days.

Fair point, and indeed I do, but it doesn't require me to live in a sealed room.

You also get a lot of flies in summer

Yes, also true. If they bothered me all that much, I'd probably use a fly-screen.

How do you ventilate at night?

I open the bedroom window. Do you run your HRV 24 hours a day?

What happen to the updraught convection columns in winter?

I close the window.

It's the ultimate eco-solution: as I said before, zero-energy and zero-maintenance, and it doesn't cost a bean.

Cheeble-eers

CJhaughey

Cheeble wrote: »

Fair point, and indeed I do, but it doesn't require me to live in a sealed room.

Thats the point the room is not sealed with a Ventilation system it has fresh filtered air constantly being introduced.

Cheeble wrote: »

Yes, also true. If they bothered me all that much, I'd probably use a fly-screen.

Each to their own, I don't much like flies.

Cheeble wrote: »

I open the bedroom window. Do you run your HRV 24 hours a day?

Yes the HRV runs 24/7/365 except when I am replacing filters or in a power cut

Cheeble wrote: »

I close the window.

Thats not what I was asking, A chimney can be very good ventilation system for the room it is in, that doesn't make it good all year round and it will have a seriously detrimental effect on your houses energy efficiency in colder months as hot air will be sucked out of the house.
I assume that your convection columns will be something similar?
How does fresh air get in to the room as is required under building legislation?
Through cracks in the envelope? Holes in the wall?

Cheeble wrote: »

It's the ultimate eco-solution: as I said before, zero-energy and
zero-maintenance, and it doesn't cost a bean.

Not really, they might be good in summer months but in humid conditions in winter they won't work at all without serious heat loss.
If they can be shown to be an alternative to HRV in the summer then they should be looked at in the design stage but I feel there is too much potential for heat loss, which will costs money to make:D

Do you have any examples of houses that have these features built in and operational?

Cheeble

CJhaughey wrote: »

Do you have any examples of houses that have these features built in and operational?

You mean windows that open?

I accept that there are benefits to HRV. Some of these are subjective, so that my preferences aren't right for everybody.

In Ireland, the weather varies: some days it's warm, some days cool, some days dry and some days humid. I like that. I'm typing this next to an open window, which has no running costs, doesn't use fossil fuels and doesn't generate CO2.

Whatever the benefits, you surely can't claim that for HRV? Remember that the OP was asking about running HRV in summer.

Cheeble-eers

Finn 09

Mechanical ventilation by its nature is movement of air at different speeds, HRV systems move are around your house there for i would take it that in summer because of the fact you are moving air it would not be cool air but it would be moving around your house which should make the air in your house feel less stuffy in the evening or bedtime during the summer.