Condensing or Non Condensing MHRV System

BMD

Hi,

I have narrowed my choice of MHRV system down to two options;

1. NI Company: Non Condensing, 85% Efficient, fan power 1.2 w/l/s, rigid ducting, remote control, programmable boost system, summer cooling

2. Company in West of Ireland; Condensing, 90% Efficient, fan power 0.9 w/l/s, rigid ducting, boost switches in rooms, summer by-pass

I want some advice on which might be the best system to go with. Is there a big difference in condensing and non-condensing systems? The selling point for non-condensing is that the air recirculated through the house still contains some moisture and therefore isn't 'too dry'. Does this make sense?

Also is there a big difference in the running costs for the two systems based on the fan powers and efficiencies?

Any advice appreciated

heinbloed

It makes no sense whatsoever, not with Irish humidity.

Topper74

Hi Heinbloed,

Wanted to thank you for advice you gave me a week or so ago on another thread...

I have a query on HRV's a friend of mine mentioned to me that these systems actually create more dust in a house by blowing it around the house and that if you had allegeries you shouldn't put in this system.

This is the opposite to what I have read and heard before on HRV systems. What are your thoughts on this?

heinbloed

@ Topper74:

It depends on the design and the maintenance as well as on the pollutant to be avoided.
Check with the manufacturers, describe the particular allergenes and pollutants.

gears

Does the OP mean one of the wheel type HRVs that have no condensate drain?

BMD

Yes, the system from the west of Ireland has a condensate drain whilst the other system (from NI) does not. It seems like it uses the moisture collected to control the moisture levels of the air recirculated throughout the house

sydthebeat

BMD wrote: »

It seems like it uses the moisture collected to control the moisture levels of the air recirculated throughout the house

any idea exactly how it does this???

personally i would want any waste condensed moisture exhausted as far from my incoming air as possible!!

MicktheMan

BMD wrote: »

Yes, the system from the west of Ireland has a condensate drain whilst the other system (from NI) does not. It seems like it uses the moisture collected to control the moisture levels of the air recirculated throughout the house

Imo, one of the big advantages of a mvhr system is the fact that moisture is removed from the dwelling.
Why would you want to introduce more moisture into the house? Doesn't make any sense.

fishfoodie

MicktheMan wrote: »

Imo, one of the big advantages of a mvhr system is the fact that moisture is removed from the dwelling.
Why would you want to introduce more moisture into the house? Doesn't make any sense.

Well there is probably an optimum RH for the air, because isn't one of the primary jobs of an MRHV to distribute heat in a controlled manner around the house ?

If the air had an RH of 0%, then it would be a lousy medium for transferring heat; its the moisture in the air that is doing all the heavy lifting for moving heat around. If you drop the RH too much, you're going to have to shift significantly more air to get the same temperature control.

MicktheMan

fishfoodie wrote: »

Well there is probably an optimum RH for the air, because isn't one of the primary jobs of an MRHV to distribute heat in a controlled manner around the house ?

If the air had an RH of 0%, then it would be a lousy medium for transferring heat; its the moisture in the air that is doing all the heavy lifting for moving heat around. If you drop the RH too much, you're going to have to shift significantly more air to get the same temperature control.

Incorrect. The primary role of a MVHR system is to ventilate the dwelling. The HR part is to transfer some of the heat energy content of the stale exhaust air to the fresh supply air. This is not a heating system, rather an energy efficient ventilation system.

Don't confuse RH with moisture content as RH is only meaningful when stated at a particular temperature. For example, external air at 0 degC and 90% RH contains less moisture than internal air at 20 degC and 60% RH. This is why condensate is created and needs to be drained away when the "wetter" internal air is cooled during the heat recovery (HR) operation.

gears

I think these type of units are call Energy Recovery Ventilators (E.R.V.) rather than H.R.V. If you google rotating wheel hrv you will find some links one of which I've copied a section of below

How does the heat and moisture transfer of an HRV/ERV work?


The incoming fresh air is tempered with a heat or energy recovery core. Heat is exchanged through a core that is frequently made of multiple plates of aluminum or plastic. Water vapor is transferred with a rotating wheel with desiccant material or permeable plates.

Models with heat recovery only transfer heat from the exhaust air stream to the incoming air stream in the heating season and from the incoming air stream to the exhaust air stream in the air conditioning season. Models with heat recovery and moisture recovery transfer heat and moisture from the exhaust airstream to the incoming air stream during the heating season, and transfer heat and water vapor from the incoming air stream to the exhaust air stream during the air conditioning season.