Zehnder has been dealing with this issue across the country, and newly collected data confirms our recommendation that you do not mix the two. There are two aspects of this practice that have had negative impacts on comfort, efficiency and healthy environments.
1) Heating/cooling the ventilation air – The biggest drawback here has been the tendency to over-ventilate to meet heating or cooling needs. In winter this can lead to drying out of the indoor air, and in summer this can lead to elevated humidity levels. With the exception of temperate climates (mostly NW USA/Pacific Canada), even in an extremely well built (such as Passive House) building, the loads for heating and cooling have been found to exceed the capacity for the proper ventilation air to meet heating and cooling needs.
2) H/ERVs connected to an Air Handler – These systems are usually designed with the fresh, heat recovered air supplied at an air handler, often at the return plenum. Every time the air handler is turned on or off, or changes speeds, the static pressure on one side of the H/ERV is significantly different than the other. This results in potentially serious imbalance in the system, and results in a potentially serious loss of efficiency in the H/ERV. We have data with systems fluctuating from 60-90% as the Air Handler changes speeds.
With a multitude of great options for efficient heating and cooling, it is best to separate these from H/ERVs. Additionally, this also highlights the need to commission and balance H/ERV systems.