2013 12 19: the energy recovery ventilator (erv) and the heat recovery ventilator (hrv) are installed. these are appliances that exhaust stale air from the house and replace the air with outside air. when it is cold outside, they do this so that the heat from the exhausting air is transferred to the incoming air with the opposite happening when it is hot outside. in principle it would be like passing the exhaust air through a radiator core while the incoming air flows through the fins; but this is not the configuration that the units employ. the efficiency of the heat transfer is remarkably high. zehnder, the company that supplied my units, has an hrv that is 93% efficient. the erv also transfers humidity, which is especially helpful during maryland’s humid summers, keeping the dryer air inside dry even though humid outside air is coming in.
i purchased zehnder hrv and erv from aubrey gewehr of zehnder america. aubrey provided excellent sales and technical support on what i believe are the best available hrvs and revs. if you have an interest in these units he can be reached at 603-422-6700 or at www.zehnderamerica.com
if you contact him, i believe you will be pleased.
in my application, the erv is used to exhaust stale air from the house and replace it with fresh air. i understand that this is a necessity in my house because it is so tight. if this were not done, carbon dioxide could build to an uncomfortable, perhaps even an unsafe, concentration.
the hrv is used differently than usual to solve a bit of a dilemma. leed requires that the air above the cooktop be exhausted to the outside at a minimum rate of 100 cubic feet per minute. we were not able to find any valves that could tightly close the exhaust duct to the outside. in addition, to do this in such a tight house requires make up air; again with no valve available. so we thought to use a kitchen hood from the vent-a-hood company, http://www.ventahood.com, in conjunction with the hrv. this hood normally recirculates air. it is special in that it actually removes grease and smoke from the air. this is in contrast to most recirculating hoods, which are minimally effective at best. we will not use the hood in recirculating mode, instead we are ducting it to the hrv in the hopes that the exhaust from the cooktop will be cleaned enough that it will not foul the hrv. the hrv will also provide make up air. so far as we know, this will be the first time such an arrangement has been employed. wish us luck.
the first picture shows the erv. to its right is the geothermal heat exchanger. it is connected to a loop of tubing in which an anti-freeze solution circulates and which runs under ground. so the incoming air temperature is passed through a heat transfer that is at 55 fahrenheit, the ground temperature in maryland in both summer and winter. overall, this improves the efficiency. it also prevents freezing at the erv air intake during the winter. the large grey tube exhausts the air. on top of the erv is a muffler and manifold. on top of the manifold are white ducts that either exhaust air from the bathroom and kitchen or send air to the living area and bedrooms. the second picture is a wider view of the equipment. the third picture shows the air supply from the erv in one of the bedrooms. the fourth picture is the hrv.