No Condensate from MVHR?

[Timpal]

Hi,

 

Have been browsing the site and there seems to be a lot of collective knowledge here - so hope someone may be able to help!

 

I DIY installed a MHVR system in our house a two years ago.

The first winter I had a steady stream of condensate out of the machine.

This (second) winter there is zero condensation and I cannot work out why.

 

So if anyone could shine any light on what this issue might be - or indeed if there isn't one I would be very grateful.

I've added some detail below - let me know if anything else if missing.

 

Many thanks

 

Tim

 

 

Today I've checked some figures in the house to try and understand what is going on:

Temperature inside 22 degrees C. RH 55%.

Outside temperature 8 degrees C (its been lower and still not had any condensation even when its below 0C outisde).

To me this would seem to be hitting the dew point and therefore causing condensation?

 

MHVR is a Vent-Axia 438222 Sentinel Kinetic

The filters are clean, the heat exchanger recently cleaned out.

There is no evidence of any water inside the machine.

I've checked the condensate drain and its not blocked (if I pour a tiny bit of water into base of machine it comes out the drain).

The heat exchanger seems to be working fine - incoming air is appox 21.5 degrees C.

Summer bypass is off.

 

To give a bit of background to the space/ set up:

- its a very simple set up - unit serves a two year old extension (75m2 kitchen, living, dining are).

- one extract, one fresh air. Insulated ducting to outside. Unit is in the warm space.

- air tight but beathable structure (lime render/ insulation on wood fibre/ timber frame).

- air flow at 30%.

 

[Ed Davies]

Any idea what the indoor RH was the first winter? I'm thinking it might have been a lot higher than this winter as the fairly newly built structure was drying out.

 

Also, have you checked what the exhaust air (from the exchanger to the outside) temperature is? Technically it ought to be condensing but not hugely. Rough rule-of-thumb calculation says condensation should start at about 13°C from 22°C, RH 0.55.

 

PS, welcome to the forum!

Edited December 23, 2019 by Ed Davies

[Temp]

I've never seen any come out of ours in 13 years.

 

Wasy your house still drying out the first winter?

[Timpal]

Yes house was def still drying out the first winter. Don't have any humidity readings, but was getting condensation on the older window frames.

Reassuring to hear I'm not the only one not getting condensation.

 

I'll double check the external air temp, just to make sure..

 

Thanks

[ProDave]

My Mitsubishi mvhr does not even provide you with a condensate drain point, they "know" there never will be any so don't provision for it.

[PeterW]

1 hour ago, ProDave said:

My Mitsubishi mvhr does not even provide you with a condensate drain point, they "know" there never will be any so don't provision for it.

It’s because the Lossnay units are fitted with a paper type enthalpy heat exchanger core. It allows transfer of humidity between the air flows. 

[dpmiller]

I had our VentAxia draining into a bucket for some months, only getting the final drain sorted recently. A good few litres a week...

[SteamyTea]

9 hours ago, PeterW said:

enthalpy heat exchanger core

https://www.engineeringtoolbox.com/mixing-humid-air-d_694.html

[PeterW]

Example here 

 

https://www.paulheatrecovery.co.uk/components/moisture-heat-exchanger/

[Ed Davies]

Why would you want humidity recovery like that in the UK? In, say, New Mexico it'd be a really good idea but not here most of the time.

[SteamyTea]

2 hours ago, Ed Davies said:

Why would you want humidity recovery like that in the UK

I have wondered that too.

Also, I know they claim that odour is filtered out, but is it really?  Could I smoke a French Woman (Gauloises) who is cooking my curry supper without the smell getting into the bedroom?

[A_L]

3 hours ago, Ed Davies said:

Why would you want humidity recovery like that in the UK?

 

As outside temeratures fall towards freezing balanced MVHR systems increasingly become unbalanced MEV systems to prevent condensation in the outgoing side of the heat exchanger freezing. Obviously this affects the energy recovery and probably occurs quite frequently.. Removing water vapour from the outgoing air reduces the temperature at which this has to occur to where it becomes a minor contribution to energy requirements. Link says reduction to -6°C

 

http://waermetauscher.paul-lueftung.de/en/product-information/enthalpy-exchangers-erv.html

[Ed Davies]

That link redirects to an office365 URL which doesn't work. It's not a leap year yet so I don't know why.

[SteamyTea]

1 minute ago, Ed Davies said:

That link redirects to an office365 URL

It works fine for me.

But the other day I count not open some links, but others could.

So maybe it is the forum software that is at fault.

 

Not sure what a leap year has to do with it, or would that be Office366

[Ed Davies]

Yes, the leap year comment was a joke - I assume that site fails for one day every four years (except…).

 

I don't think it's the forum software; the 301 Moved Permanently redirect comes from waermetauscher.paul-lueftung.de. outlook.office365.com then 404s.

[DamonHD]

Ah, as a user of O365 I was rather looking forward to it working entirely properly and intuitively one whole day in each 4 years...  Darn...

 

[A_L]

3 hours ago, Ed Davies said:

That link redirects to an office365 URL which doesn't work.

 

Obviously works fine for me!

 

Here is the relevant claim

 

Quote

Because of the characteristics of the polymer membrane it's possible to operate the devices at an outside temperature of -6°C without having any frost. Defroster or ground heat exchanger can therefore left out in regions with moderately cold climate.

 

Paul claim recovery of 60-80% of exhaust water vapour.

 

Here is web page as pdf

Paul ehthalpy heat exchanger2.pdf

Edited December 28, 2019 by A_L
to add pdf of link

[joth]

5 hours ago, Ed Davies said:

Why would you want humidity recovery like that in the UK? In, say, New Mexico it'd be a really good idea but not here most of the time.

We were recommended to have one back when we were planning forced air (fan coil) heating upstairs. It also resulted in a very slight PHPP improvement, so I didn't think much more about it. If it needs more frequent replacement, and costs more, and we're not thinking we'll need forced air heating now (rely on downstairs UFH only) maybe I should look again and remove it from the spec. 

[Ed Davies]

When the outside air is cold and dry (low RH) an enthalpy recovery exchanger will do noticeably better. When the outside air is near saturation anyway a standard exchanger with condensation happening will do nearly as well, won't it? If not, why not?

[Hastings]

I had a long talk with one MVHR supplier based in Scotland specifically about moisture as I wanted clarity on whether MVHR did or did not act as a dehumidifier. I never really understood the reasoning for his answer "yes, under all circumstances". This topic opens up the same question, I think.

 

For the house I am on the cusp of fitting a new MVHR system into, in a generally high humidity (all year round) climate of seaside west Scotland, I want the driest possible air entering the house, so definitely no enthalpy type exchanger required.

 

But I was also under the impression that the condensate created by a standard MVHR heat exchanger was moisture coming out of the exhaust air (inevitably as the result of cooling) and that the incoming air was simply always carrying the same moisture level as air outside the house. So how is very moist air entering the MVHR on a rainy day in summer going to be able to leave the house carrying more moisture than it entered with, assuming the temperature inside and outside the house are pretty much the same (and that nobody is at home producing extra water vapour)?