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HVAC: Unraveling Mysteries


HVAC: How Air Source Heat Pumps Work

Most of the heat pumps you’ll see are splits: they have an outdoor unit and an indoor unit. Occasionally, you’ll come across a packaged system where everything – compressor, condenser, coil and fan – is in a single (outdoor) cabinet.

Heat pumps do two jobs, at least in Illinois (the heating isn’t needed in tropical climes): they heat the place during winter and cool it in summer.


The way a heat pump works in cooling air during hot periods is very similar to how air conditioners operate. What does the cooling is the action of converting a liquid to a gas. The liquid/gas is the refrigerant – a hydrofluorocarbon (HFC), which these days is almost certain to be non-ozone forming (though there are still plenty of older units around that don’t have that environmental protection). The evaporator coil is in the indoor unit; it transfers the warmth (in the form of gaseous HFC) and humidity you don’t want inside the house to the outdoor unit (which is why those units are so hot in summer) and the condenser and compressor in the outdoor unit expel the heat and convert the gas back into a liquid to return indoors and keep repeating the cycle. The liquid, meanwhile, drops into a tray in the outdoor unit and is fed into a drain.


To do its winter heating job, the heat pump simply reverses direction. It’s important to understand that cold winter air is only cold to humans, plants and animals – being cold doesn’t mean it contains no heat. In fact, all air warmer than absolute zero contains some heat (otherwise, of course, it would be AT absolute zero), so what the heat pump does is to extract heat from the outside air by evaporating the refrigerant. That warmed air is passed to the inside unit and – hey presto – the house is warmed!

Need advice on choosing the right HVAC set-up for your needs? If you’re anywhere near Elgin, Illinois, give us a call. That’s what we’re here for.

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