OK, lets talk HVAC! I decided that the first discussion dedicated to Heating and Cooling, should be about the most basic central component of any system – the heat exchanger. What is that, you ask? Well i’m glad you did.
As you likely already surmised, what a heat exchanger (hereinafter referred to as HX) is, can be found by simply studying the name: it “exchanges” heat – that is it passes heat (or cold, a lower level of heat) from one medium to another. A medium is simply the air or water you are heating or cooling, or the “products of combustion” from your fire. In commercial systems the mediums may be an antifreeze mixture, steam or other possibilities. Let’s look at a few examples to help you get a better idea of what’s going on.
Example: your typical home furnace burns fuel, then passes the “products of combustion” through a HX to the chimney, or more often these days to a sidewall vent using a forced blower. On the other side of the HX the furnace uses a blower to force the air from your home through and it picks up the heat the “products of combustion” are giving up, increasing the temp in your house.
Example 2: your window air conditioner forces freon to evaporate inside a HX with your room air blowing across the other side, the room air gives up heat and the freon changes from liquid to vapor (evaporates or boils). The AC moves the warm vapor to a second HX while increasing the pressure, which increases the temp – while outside air is forced over the other side which picks up the heat and discards it to the outdoor air. Meanwhile your room air is returned to your room with less heat – that nice cool breeze is why we pay the electricity to run the AC.
Example 3: your boiler burns fuel and discards the “products of combustion”, but not before putting them through the HX – the heat passed into the water that circulates through another set of HXs, your radiators or baseboard heaters. The room air moves through the radiators by “convection” and warms the house.
So you see, “heat exchangers” are all around us. They are our friends. Without heat exchangers we would all still have to burn our fuel in a fireplace, possibly get the “products of combustion” into the air we breathe and soot up the house, to say nothing of the fact that when you leave the area of the fireplace, you leave the heated area.
A word about “products of combustion” – that is a term for the mixture of soot (carbon) CO2, CO, water vapor and excess air that comes off a fire in varying amounts. The mix is determined by many factors that we won’t get into here. But lets just say we want it removed from the living space for health reasons after we take as much of the heat out as possible.
Congratulations! you now understand (you do understand, don’t you?) the basis of all heating and cooling equipment. The heart of every furnace, boiler, air conditioner, chiller, fan coil etc is the Heat Exchanger – keeping mediums separate while passing energy between them.
