MHRV

[Richard Owen]

We're a long way from doing this, but one day we're going to have mechanical heat recovery ventilation.

It popped to the top of my thinking because I was putting in the air intake ducting before making good the bathroom wall.

I spent a few minutes scanning the interweb for the various bits and got a bit depressed because all the inexpensive units have horrendous (to me) power consumption and all the units with measly power consumption are very expensive.

Does anyone know of an inexpensive MHRV system that's cheap to run?

Alternatively, how easy would it be to rip out the high consumption fans in a cheap unit and replace them with efficient DC fans?

Anyone built one from scratch?

[Justme]

I have also been pondering this. As we use minimal power I,m not sure even the dearest would fit in our power budget.

Do you run them 24/7/365 ? Or do you run them as needed during the day/week/year?
What level of air movement / changes should you be looking at?

Can you "zone" them like heating so areas are ventilated only when in use?
Like after a bath / shower & whilst cooking or using bedroom at night but not in the day.

What realistic heat recovery can they make & can you reduce your heating systems capacity because you have one?

[stephend]

I plan to use one for an off-grid home, so energy consumption is top priority and so is price.  This is what I've found so far:

• Ventaxia HRE350, 16w total on low power, £1550 from here: http://www.dealec.co.uk/acatalog/vent_axia_hre350_range.html
• Helios KWL 350 EC, 30w on low power, £1572 from distributors
• Innoair 255 DC, passivhaus certified, 15w on low power, 2600 euros

More manufacturers here: http://www.passivhaus.org.uk/index.jsp?id=738

Ventaxia do a few exchanger units without fans; towards the bottom of this page: http://www.ventaxia.co.uk/products/category.asp

[PhatBob]

I too am thinking of this as the next step... But I'm looking at the possibility of retro fitting it into a 1972 house, which I'm told is not possible.

[Richard Owen]

Do you run them 24/7/365 ? Or do you run them as needed during the day/week/year?
What level of air movement / changes should you be looking at?

They are designed to be on all the time. Most models have different power levels, so you can set them to boost during cooking for example.

Air changes are quoted as being between 0.5 and 0.7/hour.

Can you "zone" them like heating so areas are ventilated only when in use?
Like after a bath / shower & whilst cooking or using bedroom at night but not in the day.

What realistic heat recovery can they make & can you reduce your heating systems capacity because you have one?

Zoning is difficult. And a lot more expensive. Getting registers and/or baffles to open and close based on a set of inputs is a lot of work. Or money. Or both.

Most MHRV systems are set up to just move air through the house all the time.

Most systems reckon they can recover about 70% of the heat in the exhaust gas. Some claim to recover latent heat and have a condensate drain.

I read somewhere that it's about 1KW of heat that's saved/recirculated. Which is fine if your heating load is already low.

[Richard Owen]

I plan to use one for an off-grid home, so energy consumption is top priority and so is price.  This is what I've found so far:

• Ventaxia HRE350, 16w total on low power, £1550 from here: http://www.dealec.co.uk/acatalog/vent_axia_hre350_range.html
• Helios KWL 350 EC, 30w on low power, £1572 from distributors
• Innoair 255 DC, passivhaus certified, 15w on low power, 2600 euros

More manufacturers here: http://www.passivhaus.org.uk/index.jsp?id=738

Ventaxia do a few exchanger units without fans; towards the bottom of this page: http://www.ventaxia.co.uk/products/category.asp

That's about the same as I found. I also had a look at the nu-aire units. Low power but I couldn't find any prices, which made me think they'd be towards the top end.

[Richard Owen]

I too am thinking of this as the next step... But I'm looking at the possibility of retro fitting it into a 1972 house, which I'm told is not possible.

For a comprehensive system, you'll need to run ducts to most of the rooms.

It's certainly possible to retrofit, it's a matter of how much disruption you want to go through.

[Justme]

Good links Stephend thanks. Will be about £2k then with pipes & bits.

Thanks for the other replies too.

[PhatBob]

For a comprehensive system, you'll need to run ducts to most of the rooms.

It's certainly possible to retrofit, it's a matter of how much disruption you want to go through.

Well downstairs the WBS keeps things toasty so I'm not too worried about ducting air down here.  But we have a central(ish) column that was used for the hot air heating, that has an outside air feed, and joins the kitchen, bathroom and airing cupboard - if I treat upstairs as if it were a bungalow, and ducted the warm clean air to the four bedrooms then that would surely be a gain, two of the rooms have the rads turned off during the winter and the warm fresh air would benefit things.

[dhaslam]

I had a system installed when the house was built.   Power usage is supposed to be 100 watts but I haven't checked it.   It has sensor to double the fan speed when moisture is sensed but I think the sensor only works for rooms near the unit.   It does remove a lot of moisture, something like a bucket full each week.  Incoming air stays at about 18C in the winter, which is similar to the average house temperature but it doesn't  seem to heat the house much when for example the condenser drier is running in the utility room.   At present outside temperature is 12C and incoming temperature is 21C.  An air change every hour or so is not very effective for the kitchen or the smaller bathrooms but for other rooms it is good.  The air inlets are very small only a circular opening of about one mm wide and 100 mm diameter circle.   This is how the flow is balanced between rooms, the pipes are much larger than the sum of the area of openings.  It would be much better if the flow could be controlled in individual rooms.     

[pcmadman]

We have two such boxes hanging in our house. With condensing I guess, because there's a drain coming from it. They were installed when we renovated the whole house, somewhere in early '01. I measured them recently and they pull 21W on low up to 90-something on max. But we have two and on is for the Bathroom, kitchen and bedrooms, the other is for guest bed- and bathroom and some other areas that are less frequently used, so I put it on a timeclock wich switches it on and off every 30min. That's plenty of air moving for me! Well, that's how we zoned them, but then we live in a rather large house...

But I'd definetly go for MHRV because it has one huge other advantage: They (or at least ours and yours should to) have an air intake filter. This filters out significant quantities of dust. That's clean and healthy! This does really work. I notice it whenever I open on of our computers. Compared to other peoples computers I fix ours collect very little dust. Also my brother often opens his window for a fresh breeze (his computer room doesn't have mechanical ventilation) and his computer collects way more dust. And that's even though I'm sitting on carpet and he is on wood.

(disclaimer: We also have a central vacuumcleaner and the central air heating filters as well)

[martin W]

How do the economics of these things work out?

If its only recovering around 1kWh of energy and its on 24/7 at 20 watts drain, is only saved around 0.5kWh energy per day? And my thoughts are in the summer you don't really want it putting more heat in the house - do you So if the fan(s) where using 40 watts you would not actually recover any energy.

I can understand and appreciate the improved air quality aspect, also that in the winter if the moisture level in the house is lower then you should be using less energy to heat the home. I seem to remeber form somewhere that warm dry air feels warmer than warm damp air.

I currently have an extractor fan in my kitchen above the cooker vented to outside, would you connect this to a MHRV instead of outside? Any extra filers etc? Could you piggy back this sort of system so that the extractor fan was turned on in the kitchen when cooking and pushed more air into the MHRV?

As you can tell from my post I know chuff all about MHRV and am curious....

[billi]

Hi that thread made me think

I wonder how good heat recovery systems are with an integrated heatpump

http://drexel-weiss.at/?p=f4is77j-f0is1l133j-f1is56l120j-f2is75l142j-f3is78j-f5is3j-lng1-l142

http://www.stiebel-eltron.de/en/privatkunden/erneuerbare-energien/produkte/lueftung/lueftungsgeraete-mit-warmwasser-waermepumpe/lwa-252-sol/

To boost the warm air to a higher temp

And suck air into the rooms through a piped  underground soil collector

if you have a room with a wood burning stove a  and the room gets warm enough you could then heat your water  for the rest of the house    or cool your house in summer to produce hot water ....
Would save a few quit on other expenses in the house


Billi

Ah.... here is a heatrecover system  for single rooms  only in German but needs about  2 watt when circulating 30m3 or 5 watt  at 60m3 per hour  has a air filter and heatexchanger inbuilt

i think i read about 800 euro

http://www.heliosventilatoren.de/pdf/helios_kwl_ec60.pdf

[pcmadman]

How do the economics of these things work out?

If its only recovering around 1kWh of energy and its on 24/7 at 20 watts drain, is only saved around 0.5kWh energy per day? And my thoughts are in the summer you don't really want it putting more heat in the house - do you So if the fan(s) where using 40 watts you would not actually recover any energy.

I can understand and appreciate the improved air quality aspect, also that in the winter if the moisture level in the house is lower then you should be using less energy to heat the home. I seem to remeber form somewhere that warm dry air feels warmer than warm damp air.

I currently have an extractor fan in my kitchen above the cooker vented to outside, would you connect this to a MHRV instead of outside? Any extra filers etc? Could you piggy back this sort of system so that the extractor fan was turned on in the kitchen when cooking and pushed more air into the MHRV?

As you can tell from my post I know chuff all about MHRV and am curious....

Well, you need to ventilate anyway. In older homes it's automatic because of the bad isolation, but in newer homes the air exchange with outside is just to little to live in. So it doesn't matter, I need to run a fan and one with heat recovery just seems to make more sense.

In the summer you say, you don't want it putting more warmth into the house, well then you need MHRV, because it also works the other way round; If the inside air is cooler, it will cool the outside air it's taking in. It has the effect of isolation on ventilation.

No, high moisture levels actually make the air feel hotter. That's why air-conditioning dries the air. This is because sweat vaporises less in moist air.
See for more: http://en.wikipedia.org/wiki/Air_conditioning#Humidity_control

And about connecting the extractor fan from the kitchen, I was wondering about that to. Not exactly the kitchen, but the exhaust from the tumble-drier is now going directly outside because the air is very moist and hot, but if this went trough the MHRV we could recover a significant amount of heat I recon.

[Richard Owen]

Lots of MHRV systems explicitly don't let you connect a cooker hood. Something to do with it greasing up.

Some do, but I suspect the filters will need regular attention.