Posted By jumpingspidermedia on 06 Mar 2011 09:45 PM
If you use a heating system more often than air conditioning, you need an HRV. If the opposite is the case, an ERV is recommended.

Posted By guy_davis on 25 Mar 2011 03:34 PM
As a point of reference for the original poster's question, we built a tight (1.5 ACH @ 50) home in Calgary which is very dry in the winter.  House is heated via radiant in-floor so we have no active house-wide humidification. All the advice we received was to go with an HRV as we'd have more then enough humidity, but after moving in we found the humidity dropping below 20% when it got cold out (below 5 deg. F).

So, we paid more to get ERV cores installed into our HRV unit in hopes of retaining more moisture, with little impact.  As well, when it gets really cold we dial the runtime of the *RV unit down to running just 20 mins every 12 hours.  The VanEE unit we have is supposed to have a "Smart" mode that takes care of this automatically, but we found it would run faster/more whenever the humidity level got near 30%, ensuring the house was always dry.

Now we manually control the *RV runtime and run in-room humidifiers each night in all four bedrooms.  Even with this, we're lucky to hit 35% humidity in the house @ 32 deg. F outside.  It's much drier when it's really cold.  So, if you live in a really dry area and your family isn't taking showers multiple times a day, then be careful with dryness.

     

Our current status with ERV cores is found at: http://welserver.com/WEL0381/

Isn't Calgary wonderful!! Reading between the lines I would assume there is at least four people in the house and the house while a nice size, is not huge. So still not having much humidity inside speaks volumes about our dry atmosphere. We have been a bit colder this year than the last five or ten so this wrings even more moisture out of the outside air. This is one reason you can't run hrvs of humidistats. They would never come on in the winter. Is it possible to slow the VanEE down at all or are you already running at the slowest speed? As its a new house, even though I'm sure you picked the best products available, I would still be concerned about out gassing. Normally I would say try for .25 air changes per hour of occuppied time but this would really dry you out. Sure would hate to see health issues due to contaminated air even if there is no humidity issues. You might try growing lots of indoor plants which will increase the moisture and some are very good at harvesting pollutants. I believe Olds College has some good data on this. Some people in the area also run small fountains that sound nice which help a bit. As with humidifiers watch for contaminates in the water.

Next point – an ERV will transfer a percentage of the moisture from the higher moisture content air stream to the lower moisture content air stream. Ours say is – 40-60% given the conditions present. Do not confuse this with humidity ‘control’ or with relative humidity. Relative humidity is related by temperature, and when you discuss ERV’s and their transfer of moisture – it is absolute humidity, or specific humidity that needs to be looked at. SO- 40-60% of the humidity will stay where the humidity is highest, and the other 40-60% will be sent to the other air stream – be it inside or outside. More simply – an ERV is still dehumidifying when the outside air is more dry, and still humidifying when the outside air is more ‘wet’. Just not as fast as an HRV – and fast being defined as the latent (moisture transfer) of 40-60% in this case.

The moisture recovery from a bath exhaust – considering the amount of time during the whole day this would apply – is not significant to the overall picture. And it depends on your climate, and your house as to when the transfer of moisture would be beneficial or not beneficial. But- as stated, it is a minimal impact considering the fact that the bath exhaust time is very little compared to the time it is ventilating the house and the bath is not in use.

So – if you had a unit that you could say – turn moisture transfer on and off (which is not available in the market), this would be ideal. Else – you have to weigh the entire operational time – and conditions present as to how much moisture transfer (or none) would be ideal. And this is what we have done. From an energy saving performance standpoint – And ERV with 40-60% transfer will be about as good as you can get in a mixed climate location (most of the US)… and even so in a non mixed climate.

Contamination - ASHRAE deems up to 10% contamination is fine in residential applications – even for bath exhaust. This is not really an issue – ventilation is always diluting. The competition does things like “recirculation defrost” – more simply put – 100% cross contamination (we don’t)… but cross contamination is not a big deal. If this is still a worry – example – 3% cross contamination… then increase the ventilation flow by 3%... and now you have the same amount of fresh air as if it were 0% cross contamination.

Durability is directly related to the exchange media design/material, not necessarily that it is an HRV or ERV. We do moisture transfer with a polymer material that is washable and replaceable. There is no getting around service of a E/HRV core. Without yearly service of some kind – operation and performance will be negatively affected. Our design ensures the best operation and life – given the worst of service on the core, or neglect on the installation. But – even with that said – no service will result in failure within the first 3-4 years no matter what E/HRV you install.

So – you have a choice – Install an HRV or an ERV. There are only two technologies… and since we cannot ‘regulate’ the amount of moisture transfer on the fly… you have to decide which is going to work the best. Looking at just moisture transfer as related to energy savings in the home – some amount of moisture transfer will generally outweigh not having it. After this decision – you then compare heat transfer efficiency, watt per cfm (power to operate the unit), air filtration, and service/installation cost. When you weigh all of this in to the picture – our unit will shine.

Air Filtration Systems

ASHRAE deems up to 10% contamination is fine in residential applications-even for bath exhaust.

But if you run the AC via dehumidistat control it'll stay comfy & healthy, with an HRV, but at a boost in energy use. In a higher-R house with low sensible AC loads dehumidification control becomes critical, and an ERV helps.

Posted By Dana1 on 04 Feb 2011 04:01 PM
ERVs don't return humidity super-efficiently in cool weather, but they return some, allowing you to run a higher ventilation rate without excessive drying. There's little down-side to going with ERV, and since you can run higher winter ventilation rates there is a slight health-factor benefit.

Dew points are low enough in summers that you don't benefit a whole lot from ERV during the cooling season though- your sensible cooling loads far outstrip your latent cooling loads. The fact that your WaterFurnace condenses a bit of water in the summer isn't an indication of a NEED to dehumidify. No matter how dry the summer air is, the dew point above the temp of the cooling coils of a compressor system, and you'll get some condensation out of it. But the volume of water condensed is much much lower than in places where the dew points are well north of 70F (where the latent load is more than 80% of the cooling energy use for the incoming ventilation air.)

If can air-seal the house sufficiently to get your air changes per hour @ 50 Pascals (ACH/50) in a blower door test down below 2, you would almost certainly be able to maintain 30% RH indoors all winter without active humidification. The fact that it's dropping below 20% unless you actively humidify it's an indication that your natural ventilation rates are relatively high, and the argument for active ventilation may be moot. Houses that are PassiveHouse tight (<0.6 ACH/50) always need active ventilation to bring the humidity DOWN to 30% in winter. Canadian R-2000 standard (<1.5 ACH/50) homes can also be in the same situation. With cooking/bathing/breathing for six the amount of moisture introduced by your family SHOULD be able to keep it at 30% and then some.

With "natural" ventilation the infiltration/exfiltration points are somewhat random, and don't guarantee that the ventilation air is distributed where it's actually needed. Ventilate with an ERV, yes, but DO try to get the natural ventilation rate down- it'll save heating/cooling energy, and you'll end up with better indoor air quality overall. Tightening up the house to the point that you can decommission the humidifier and run the ERV in winter under dehumidistat control would be ideal.

I use this:  HEPA filtration and energy recovery ventilator, Broan GSEH3K.  True HEPA filter with a 99.97% efficiency on particles ≥ 0.3µm.  Pre-filter with a >90% efficiency on 3.0 - 10µm size particles which extends the life and performance of the HEPA filter.  HEPA filtration capability: 270 cfm; fresh air capability: 70 cfm – 110. The Broan GSEH3K tempers fresh air with outgoing stale air to minimize energy expenditures.