Humidity and MVHR

[HerbJ]

 

I agree with @peterw.

When I was getting proposal for my MVHR, the cost of the Enthalpy HE was only £350( excl VAT) extra to the standard HE. This was for a PAUL 450 MVHR unit,  a large volume and relatively expensive unit. The cost of a replacement enthalpy HE from Germany for about 850 Euros, at the time.  So, I am a little surprised at the costs being quoted to you for replacing your HE. 

 

There is no labour involved. it will be simply taking out one and fitting the other back in its place  - just like  the routine cleaning and maintenance for the HE. There is no set up work or adjustments to be made.

[lizzie]

I had individual prices for items needed, heat exchanger and sensors etc  and I added it all up and then a bit for labour came out to £1200 ish which in reality means £1500 ish if the last 2 years are anything to go by!

 

Agreed it would have been much better and probably cheaper to have done it at the start ....looking back I mentioned humidity control when speccing system.  I didnt notice it had been dropped in final decision making. I relied too much at that time and didnt question things as much as I now know I should have.  

 

Its not installers or suppliers fault I should have picked it up and reinstated it.

Edited May 23, 2018 by lizzie

[PeterW]

12 hours ago, lizzie said:

R I had individual prices for items needed, heat exchanger and sensors etc  

 

@lizzie as @HerbJ says this isn’t something that needs - or should have - anything changed in a balanced system. The difference is the material the HeX is constructed of which allows vapour diffusion rather than like the existing plastic film unit you currently have. 

 

A lot of the humidity sensors are designed to trigger boost speeds at higher levels of humidity. They have no reverse function to slow the fans or increase humidity so would be fairly pointless. 

[lizzie]

@PeterW thank you I  appreciate this input it is so helpful. I am pretty stupid with all this stuff I thought I as sensors came on the list I needed them!

[Dreadnaught]

Prompted by this discussion I have been reading-up on enthalpy heat exchangers and am now considering specifying one for the MVHR in my build. The marginal cost of having one is of course much reduced if specified up-front. Targeting internal comfort as I am, it seems like a worthwhile extra spend to consider.

 

I learnt that:

1. an enthalpy heat exchanger is the same shape and form as a typical metal heat exchanger but just made of a polymer material, which is somewhat more costly to manufacture. As has been said before, they are a 1:1 substitution. No labour required.
2. some earlier designs of polymer heat exchanger, ones based on cellulose (like paper), had a finite life but more modern ones seem to last indefinitely.
3. the polymer membrane is selected to prevent any larger molecules than water, such as most air pollutants or pathogens, passing.
4. enthalpy heat exchangers are less efficient at heat exchange than their metal brethren (by about 9%) but the increased humidity levels indoor mean a latent heat gain due to the reduced evaporation losses. This "closes the performance gap" in terms of energy recovery between the two systems.
5. typical moisture recovery rates are about 65%.

Slightly off topic on the subject, might having an enthalpy heat exchanger reduce the potential for winter freezing of the MVHR and so reduce the use of the pre-heater designed in all units to prevent it? Reasoning being: intake air will be low humidity already in winter but exhaust humidity will be much reduced, reducing icing.

Edited May 24, 2018 by Dreadnaught

[HerbJ]

3 minutes ago, Dreadnaught said:

Slightly off topic on the subject, might having an enthalpy heat exchanger reduce the potential for winter freezing of the MVHR and so reduce the use of the pre-heater designed in all units to prevent it. Reasoning being: intake air will be low humidity already in winter but exhaust humidity will be much reduced, reducing icing.

 

 I believe this the case and you may be able to save the cost of the pre-heater, if the enthalpy HE is fitted. I couldn't do this on the PAUL Novus 450 because the preheater was not an additional unit that but part of the standard design and included as part of the MVHR unit.  This may be possible on some MVHR units, FOR which the preheater is an "extra" feature and installed separately. 

[A_L]

2 hours ago, Dreadnaught said:

Slightly off topic on the subject, might having an enthalpy heat exchanger reduce the potential for winter freezing of the MVHR and so reduce the use of the pre-heater designed in all units to prevent it? Reasoning being: intake air will be low humidity already in winter but exhaust humidity will be much reduced, reducing icing.

 

1 hour ago, HerbJ said:

 

 I believe this the case and you may be able to save the cost of the pre-heater, if the enthalpy HE is fitted. I couldn't do this on the PAUL Novus 450 because the preheater was not an additional unit that but part of the standard design and included as part of the MVHR unit.  This may be possible on some MVHR units, FOR which the preheater is an "extra" feature and installed separately. 

 

@Dreadnaught & @HerbJ Yes it should also prevent loss of heat exchange efficiency when temperature falls below zero in winter, down to -6°C according to Paul. I am sure at one point Paul claimed down to -20°C.

 

Repeating the links I gave in an earlier post on this thread.

 

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

 

                        Edit: no longer seems to work    http://waermetauscher.paul-lueftung.de/en/product-information/enthalpy-exchangers-erv.html

                        2nd Edit: @Dreadnaught managed to get a copy and saved as PDF

PaulenthalpypageasPDF.pdf

Edited May 24, 2018 by A_L
as in text

[Dreadnaught]

2 minutes ago, A_L said:

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

 

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

 

 

Second link is broken for me.

[PeterW]

good article here about paper vs plastic or foil HeX cores

 

http://www.air-creation.co.uk/uploads/files/Downloads/Lossnay Brochure.pdf

 

Most - not all - commercial units are paper as they don’t need to have a drain port.  

[lizzie]

@PeterW good article thanks.

 

I think the Frankishe is plastic?

 

Good news is humidity level in house is now 42% and much more comfortable.  I have mvhr fan on lowest setting, windows open (and its raining outside)

[SteamyTea]

32 minutes ago, lizzie said:

Good news is humidity level in house is now 42% and much more comfortable.

Bad news I say, I felt good yesterday and dreadful today.

 

Edited May 24, 2018 by SteamyTea

[lizzie]

6 minutes ago, SteamyTea said:

Bad news  say, I felt good yesterday and dreadful today.

 

Thats high. I would not feel good with that! About 45% is my optimum level. Which website are you using for those stats - are you able to post me a link. Thanks

[SteamyTea]

I monitor the RH and Temperatures myself.  Just a DHT22 and a Raspberry Pi.  Easy and cheap to set up.

 

You could try WeatherUnderground to find a local weather station.

https://www.wunderground.com/