PIV Systems / Heat Recovery Units

[linconhawk]

Has anyone any experience with either of these ?

Would love any feedback if you have fitted one or something similar.

Thinking about something to help with condensation / mould problems...

I have a few questions if someone can answer...

Would a PIV system make the house feel colder ? Ive read so much on the internet about these, but am still a little confused...

and am I right in thinking that one that has a "heater" built in or a "heat recovery unit" slightly warms the air, making it not so cold... My only problem with this, is that wont it increase my electric cost by quite a lot ? wouldn't it be like using an electric heater ???

Please any help / advise would be appreciated, feeling a bit confused...

TIA

 

[^woody^]

Heat recovery and PIV are solutions for different problems. You do not need heat recovery for a condensation problem.

If you live in a house, the PIV outlet will normally be above the stairs. You will feel some air movement there, and you might think it cooler if you stood directly under the outlet for several minutes. Most people will just walk up and down the stairs though, and not notice anything.

Running costs are a few pounds a year. Much less than you will spend on mould treatment and redecoration.

The unit does not heat air. It's a fan only.

But you need to be clear that this is the correct solution to your problem.

 

[linconhawk]

Thanks for the reply Woody...
So, what is a heat recovery unit and why wouldn't I need one ?
I thought I read that these are also good for condensation... ?

I have read that some PIVs have a heater element in them that can slightly warm the air... Would this be good to help the house not so "cool"...
Ps - I keep saying house.... We actually live in a bungalow....

Thanks again...

 

[^woody^]

Heat recovery is really just an economical thing so that the heat from extracted air is put back into the building to save reheating it. They are essentially just extract fans, so are not "good" for condensation, they are just the same as any extract fan.

There needs to me a significant temperature differential between the internal and external air, so that these units may well be beneficial in Scandinavia, but less so in the more temperate UK.

The heater in PIV's is a bit of a gimmick. It is better to heat the property via its normal central heating system. I can't think of any advantage of marginally heating the incoming air, as its temperature will reduce as soon as it is pushed out into the property. Better to have the heating system heat the air evenly in the first place.

PIV's do work but are really a last resort thing. Other solutions should be investigated first - heating, heating patterns, ventilation, insulation, use of the property.

 

[theprinceofdarkness]

PIV unit draw air in from the loft which is typically a few degrees above the outside temperature. So they act as a cheap solar heating system. They can contain a heater and thermostat to warm the air, I don't know why either. Apart from the direct fan electricity, they also have filters in them, else it would blow loft dust out into your hall. These might be non-cleanable so are an added cost.
In theory because the house is presurised you do not get cold drafts through small gaps in window frames, doors, etc.
Heat recovery unit suck warm moist air from within the house and transfer the heat content into a fresh air stream that then becomes warm and is distributed around the house by ducting. These also use electricity and filters and must have a small heater in them so the condensed water from air from the house which has to be drained away, cannot freeze, or the unit will flood.

 

[linconhawk]

Thanks guys...
So, it seems I need a PIV system...

I still can't get my head around the fact that the house would be cold....

I went into my loft today and it was freezing....and if this loft air is being constantly pumped around my house, surely it's going to be a cold breeze constantly in my house.....

Therefore my central heating would need to be on more..... ?

Am I missing something....?

Thanks

 

[^woody^]

Am I missing something

Yes.

It's a tiny amount of air from the loft, and as soon as this mixes with the warm air at ceiling level, the temperature difference is negligible by the time the air travels outwards.

Your central heating needs to be on as part of dealing with your condensation problem. That may well be more than you are used to purely because it was not used properly in the first place adding to the problem, and not as a result of having the PP fan installed.

Part of the assessment in fitting the fan, should be how you currently use the heating and ventilation systems. That may well solve the problem without needing this fan. You should not just have this type of fan fitted in isolation.

 

[linconhawk]

Thanks Woody....
It's all starting to make sense now....

Our heating at the moment, comes on about 4.30am off about 7.00am

Then on about 4.30pm until about 7.00pm.
Thermostat is currently set to 22.5.....

Is this setup not so good then...?

Thanks again

 

[theprinceofdarkness]

Is your loft actually colder then outside?. The drafts that sneak in are definitely from outside.
frank

 

[linconhawk]

Hi Frank,
Sorry, I don't understand your reply... ?

 

[^woody^]

Is this setup not so good then

On/off hearing patterns, and the associated temperature changes from rapid heating and cooling are a major cause of condensation. 22.5° is quite high.

It's one factor.

Have you read up on dealing with condensation?

 

[AronSearle]

To add to woody's post, you need to think about what the problem is and what the solution may be.

Cold surfaces will contribute to condensation, extra ventillation reduces this at the cost of heating outside air. Also, it does not always fix it, and additional insulation may be worth considering on some walls.

PIV systems blow air from the loft into the house, and air escapes around gaps in windows, doors etc.

Heat recovery systems suck air out of the house, and blow new air in from outside. So for this to be effective you need an very good level of air-tightness or they are just a waste of time (Its like running air conditioning with the window open). you also want the inlet and outlet to be in different rooms so you don't end up just moving air in one part of the house.

Both will effectivly reduce levels of humidity, heat recovery systems work very well with good levels of insulation (like passive house), otherwise they don't save any money (and may cost more to run than normal heating).

PIV systems are a cheap effective method, but at the cost of more money over time in wasted energy.

 

[linconhawk]

Thanks for replies guys....

Woody, if my heating / boiler setup is not ideal, how can I change this to a better setup ?

I have read up on condensation and know a lot about it, I posted last week regarding it....

We are doing everything we think we can and there is nothing noticeable wrong with our bungalow.. We are baffled... This PIV system is my last resort....

Thanks

 

[AronSearle]

Condensation is simple, no need to be baffled, cold surfaces = warmer air = condensation.

For example, if internal conditions are 20°C and 65% RH, then any surface at 13°C will cause condensation.

Lower the humidity to 40% RH, and surfaces now need to be as cold as 8-6°C before they will cause condensation (and 40% RH is about as low as is reasonable to achieve, or as low as most people find comfortable).

Crap windows, poorly or uninsulated walls and steel lintels are items which can cause excessive thermal bridges where internal surface temperatures may get near 10-6°C. If you are living in a bungalow I’d bet you have some of these features or similar.

Getting the humidity to near 40% RH with normal ventilation will be very difficult in spring and autumn without excessive ventilation. It's mild and humid in the day (when most people want to open windows), and cold and less humid/dry at night when people want to shut windows.

Constant ventilation will help, but you can see why it's a rough fix and the real problem is eliminating or reducing the cold bridges.

 

[^woody^]

Condensation is simple, no need to be baffled, cold surfaces = warmer air = condensation.

That couldn't be more wrong. The theory is simple but, in practice it's difficult to prevent, and I'd a complex balance the four factors.

There are homes were the occupants can do everything wrong and get no condensation, and others where the occupants do everything as per the "rules" and get mould all over the place.