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hvac engineer install heat recovery ventilation system

HRV/ERV (Heat/Energy Recovery Ventilator)

How does it work?

An HRV will draw air from the outside and pass it through a heat exchanger where it exchanges heat with clean air being exhausted from the building.  An ERV will do the same thing but tries to exchange latent heat energy in the form of moisture in the air as well as sensible heat energy which is measured by temperature only.   If it is 0° outside and 22° inside.  The 0° outside air is heated by the 22° air being exhausted.   

Why do we need an Air Exchanger? 

Today's building codes require the building envelop to be sealed tightly.  This saves energy by reducing heating & cooling loads but can result in a lack of fresh air for occupants.  People release a lot of carbon dioxide which builds up without proper ventilation.  A busy office can release a lot of CO2.  Anything thing over 1000 PPM CO2 can have big affects. Volatile Organic Compounds (VOC) are off gas from things like printer ink, new furniture or carpet.  Cleaning products and dishwashers release various gas. Without air exchange these gases will buildup over time. Indoor pollution can be far worse than outdoor pollution.    

What Maintenance is required?

An air to air heat exchanger consists of a series of small passage ways that can become plugged with dust and dirt if not maintained.  There are air filters on the air intake and exhaust, upstream of the heat exchanger which must be cleaned regularly.   Small HRV's, under 250 CFM, will often have foam filters that need to be washed frequently.  The filter on the intake normally clogs first, while the exhaust air, which is fairly clean will take longer to plug up. This results in a negative pressure inside the building which is to be avoided. Try to clean these foam filters every month, every 3 months if a disposable cardboard filter is used. If necessary, the heat exchanger core can usually be removed and cleaned out with high pressure air.  Check the owner manual for detailed procedures.  Air exchangers can form frost in the winter and need to be defrosted.  Each unit is equipped with a drain to an open drain location or a bucket.  It should never be tied directly to a sanitary line.   

ducted heat recovery ventilation system
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