Heat Recovery Ventilation - Loft Input?

[shockfire]

Hi all,

Wasn't sure where to post this, hopefully this will be the right place.

I have recently had mould growing in the house, so decided to look into ventilation. The house is sealed up quite tight (double glazing, cavity insulation etc) so I figured there is nowhere for stale air to go. Due to being at work all day, I'm not comfortable with leaving windows open (and at night it's too noisy outside to leave windows open) so I've decided to purchase Mechanical Heat Recovery Ventilation / MHRV.

A system such as this one: http://www.ebay.co.uk/itm/HR100R-He...tilation-Condensation-Vent-Axia-/280819016640

The output of the HRV would be directly to outside.

I read somewhere that you can take input directly from your loft / attic if it's ventilated. This would have the Winter benefit of the air intake being slightly warmer than general outdoors air, before heat recovery is performed, which would boost efficiency tremendously. I was wondering if any professionals here had done such a thing, or if you think it's a good idea.

My loft is full of (probably fibreglass) insulation - is it possible that bits of insulation (which isn't nice to breathe) could find their way into the ventilation system or am I being paranoid? Even if ducting ran to the very top of the loft space?

Also my loft has a combi boiler - I take it this won't give off any horrid gas (since lots of people have them in their living space i.e. kitchens).

I do like the idea of the efficiency boost from putting the air inlet in the loft.

Please let me know what you think

Thanks,
Shockfire.

 

[dhutch]

The boiler will almost certainly be 'room sealed' in other words the combustion happens in an air tight box only ventilated to the outside, not concerns there as long as the inlet is not near the flue.

My parents have a MVHR unit which takes its inlet from the attic space as you propose.

I dont know what the performance of the less costly MVHR units is, as you can spend £1000 on one, but as money is a bit tight and im considering fitting one to my own house will be interested on others replys.

What ducting are you planning to use, my parents system uses un-insulatued corigated alumium, with perforated 'acoustic' aluminum pipe for the last 4ft before a room to take out duct/fan noise.


Daniel

 

[shockfire]

Hi Daniel,

Thanks for the reply - interesting that your parents use a loft intake, it's starting to look like the best option. It should also remove the possibility of taking in any "freezing" air which can damage the equipment.

I'm seriously considering making my own system from scratch. Might take a while to make, but i'm in need of a new interesting project lately I've only been able to find one DIY project sofar, but it looks quite promising:
http://makeprojects.com/Project/Heat-Exchanger/279/1
...and if it doesn't work very well, it's only <£50 in materials. Might be worth a shot.

A few changes I think may be required though:
+ It probably needs thinner "panels", this suggests 19mm, I was thinking more like 5mm to radically enhance surface area
+ Needs a filter to stop the system from spreading horrible stuff around the house. Filter out pollen would be good.
+ Not sure about wood construction. Maybe plastic would be better. Or possibly gloss paint all wooden panels.

What do ya think? If it works, you'll save yourself £1000

As for ducting, I was thinking uninsulated aluminium ducting for intake from loft to ventilator, and output from ventilator to outside. Then for all connections to rooms (input and output), fully insulated acoustic aluminium ducting, to minimise any heat loss. In a fully DIY system, I'm undecided between 80mm and 120mm, I'll have to do some research. Good old ebay: http://www.ebay.co.uk/itm/3-80mm-Insulated-acoustic-ducting-10m-length-/280591802490

Thanks,
Shockfire.

 

[^woody^]

I have recently had mould growing in the house, so decided to look into ventilation. ..... I've decided to purchase Mechanical Heat Recovery Ventilation / MHRV.

You are going about it the wrong way

If you have a condensation problem, then you need to address that and not just get hold of a mechanical system which may do nothing at all for your particular problem

You've linked to the central fan unit, but what about all the ducting to every room and all the installation and making good?

Are you aware of the potential for draughts from a poorly designed and installed system?

And don't think that there is some magical cost saving of using loft air to re-heat incoming air. The different in temperature is minimal as is the time the incoming air has to receive this heat exchange from the out going air

 

[shockfire]

Hi Woody,

Thanks for your input. I'll try and answer these points.

If you have a condensation problem, then you need to address that

I have been doing some (simple) research. More specifically, the condensation problem seems to be in my bedroom. With humans breathing out for eight hours per night, the humidity levels rise upto 65% by the morning. Mould was appearing in this room (has been cleaned off now, but it will be appearing again soon). Bedroom does not have air bricks (nor do I want any). There doesn't appear to be any major condensation problems in any other room (and humidity levels average 45-50%), but I thought a whole house system will be beneficial, especially as I intend to make the house "tighter" in future. I like the idea of some fresh air in the house.

You've linked to the central fan unit, but what about all the ducting to every room and all the installation and making good?

Although I've thought about this, I simply wanted to make sure the heat exchanger was feasible first. My aim is extraction points in the bathroom and kitchen. Fresh air will be piped into main bedroom and living room. This is subject to change...

Are you aware of the potential for draughts from a poorly designed and installed system?

No. Are you able to provide any information on this? I'll get Googling.

And don't think that there is some magical cost saving of using loft air to re-heat incoming air. The different in temperature is minimal

This wasn't a priority - I just think it's better to take an intake of loft air compared to intake of outside air. Not just for the temperature reason (that's an added bonus!). This way I only have to "make" one vent for outdoor use (extraction). Also, I have been reading about the bonuses of keeping the air inside your loft fresh and circulating, taking air out of the loft will push more fresh air into the loft space. Seems like a lot of positives, with no negatives detailed sofar.

I would be interested to hear your thoughts on a custom DIY heat exchange.

Thanks,
Shockfire.

 

[dhutch]

Im need of more time not more work, so havent considered building my own unit. If you where going down that route I would suggest at minimum its going to require the heat exchanger and fans buying in, at which point you just making a box, an one that s going to be less good and have less warrenty/resale than a bought item.

We dont have any inlet ducting at all, i just sucks the air in from where it is! Simples. Obviously the temp diffrence should be minimal, but as you say, if nothing else, greatly reduced the chance of sub-zero inlet temps.

There a lot of people on here against them, and its certainly right to be sceptical of cost savings, but while only limited my experence is that they do make a big diffrence to the air quality and humidity in a house without detracting in any way. Atleast, the one in my parents house does.


Daniel

 

[^woody^]

I would say read up on condensation prevention and heat recovery issues, but having said that, it is possible to read too much and get confused with a lot of conflicting info

I could write a whole stream of stuff, but you do need to research.

Think about what you just posted ... you have a limited mould issue in a single bedroom and so what to vent the whole house. You also want to tighten up the house and then introduce forced ventilation.

I'm seeing some contradiction there, and a waste of time/money sealing and then venting a complete property (waste of heat) and merely for a single confined room issue

The loft as a source of air is a side issue which can be ignored. Deal with why condensation is occurring in that particular spot

Humidity readings are irrelevant in isolation - any house can be between 40 and 90% RH with no problems

Think about use of the property and in particular heat patterns - that alone could be your problem

And don't think that "fresh air" via a loft or this system is any fresher than any other type of air from any other source. And the concept of "heat exchange" (wow saving money) is misleading - the temperatures are just too close to be beneficial

Potentially you could get a benefit of this system for a few weeks of the year in sub-zero temperatures - and then only if you stay in the house all day long.

It's a sledgehammer/nut scenario with no guarantee at all of it being beneficial or stopping your particular mould problem in your particular property