The UltimateAir® Blog

It sounds as though you are implying ERV/enthalpic units are the only option to use. So even when humidity levels are low outdoors you are saying to always use an ERV? Even in extreme cold climates you are saying to use and ERV? Even when cross contamination is a concern you are saying to use an ERV? If you are recovering the heat from bathroom exhaust are you saying to use an ERV? Even when durability is a concern or you want to be able to rinse off bacteria with water and the ERV core is made of paper you are saying to use it? I don't understand how one technology is supposed to meet all application needs.

First off – all ERV’s are HRV’s – meaning all ERV’s transfer heat, with the addition of transferring moisture. So – If an HRV will work for your application – then most of the time so will an ERV. At this juncture you would compare the heat transfer of the units you are looking to purchase, and our heat transfer is the highest performing unit on the market. 
 
 
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.