Construction HVAC – Understanding the Basics

Understanding the Basics of Construction HVAC

Almost everyone in the construction world, and many outside of it, knows that HVAC stands for the heating, cooling, and ventilation system within a building.  The goal of any HVAC system is to make sure that the temperature inside any building is comfortable for those who are in it.  This means warming the building up during the cooler months of the year and cooling it down when it gets hot outside.
For heat, an HVAC system uses gas, oil, coal, or electricity to provide heat, while the cooler air is provided by a chiller, gas or electric air conditioner, and an electric heat pump.  Everyone in the construction field must understand the basics of air conditioning in order to fully understand any of the HVAC systems that are available.
Here are the steps of any cooling cycle of an HVAC unit:

1. Low pressure refrigerant is compressed by the compressor of the unit, which will then increase the temperature and the pressure. The amount of the pressure, as well as the actual temperature, is dependent on which type of refrigerant is used in the air conditioner section of the HVAC system.
2. The condenser will then blow outside air onto the refrigerant vapor, which will turn it into a liquid. This liquid is approximately twenty-five degrees higher than the temperature of the air outside, which is why the condenser always seems to be blowing out hot air.
3. There is an expansion valve that will change the refrigerant from its high-pressure liquid to one that has low pressure. That pressure change ensures that the temperature is lowered.
4. The evaporator within the HVAC system will let the warm air inside blow over the coils. Those coils are filled with cold refrigerant liquid and the heat from the air will turn the cold liquid to a warmer gas.  Many times, the type of refrigerant is chosen due to the amount of heat that it can change from a liquid to a gas.

There are many different HVAC systems available, but there are a few that are more commonly used in the construction field.  The ones that anyone in construction will see the most include:
Heat Pumps
Heat pumps will take the heat from the air and use it for heating, while the cooling portion works as described above.  These are generally seen as outside units, as the compressor and condenser need to be outside to draw the air in to use.  This type of HVAC system will need an electric back-up resistive heater, because the heat pump is unable to pull enough heat from the outside air when it is extremely cold outside.  This type of HVAC unit is usually chosen because it is simple to install and cheaper than every other system.  However, there are not too many control options and these HVAC units only last an average of seven years.
Roof Top Units
Roof top units are also known as packaged units and will sit on a roof or simply outside on the ground.  To heat the building, a gas furnace is normally used, but it is possible to use other types of fuel as well.  It is possible to mix the outside air with the return air since these units are outside and the air that is heated or cooled is sent into the building through ducts.  These HVAC systems are also easy to install and are fairly inexpensive.  The downside to these systems is that there are unsightly ducts running vertically through buildings.
Chillers
A chiller is slightly different from the direct expansion systems above, because they need to make cold water to distribute via pipes to the air cooling coils.  These systems will also need a boiler to make hot water to create heat via the heating cycle.  This is a two-pipe system requires a system changeover when the building owner wants to go from the heating option to the cooling option and then back again.  These HVAC systems are quite energy efficient, but they are also expensive to install and difficult to maintain.
Heaters
Furnaces provide heat and they work from burning wood, coal, gas, oil, or other fuels.  Direct fired gas heaters are an excellent option, as they use fresh air and fan distribution.
Fans and Ventilation
This option does not provide extremely cold air in a building, but they will ventilate a space to pull warm air out of the building.  This is usually done via massive wall fans, but there are other options that work just as well.
It is not always easy to determine what size HVAC system is needed.  After all, schools and office buildings will need different amounts of air conditioning and heating per one thousand square feet then a dedicated computer room or conference room will need.  Thankfully, there are specific guidelines for each space that will allow construction workers to calculate the specific needs for the space that they are working on.
Now that everyone understands the basics of HVAC systems in the construction field, construction workers can continue with their job of finding the perfect one for the project that they are currently working on.