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HVAC sizing works for a lot of people. If you are an HVAC technician or in HVAC service business, it is essential that you are able to provide the best service to your customers, or else, they may seek the assistance of your competitors. If you are the owner of a building, having even just the basic knowledge of HVAC sizing will give you protection from contractors, architects, and mechanical engineers who may just fool you into thinking that you already have the perfect HVAC system when, in fact, you do not. Furthermore, HVAC sizing has a lot of benefits.
First, HVAC equipment that are in the right sizes are inexpensive to install. More often than not, an oversize HVAC equipment uses up a lot of energy, thus increasing your electrical energy consumption. Having the right sizes can help you save energy and money as well. A right-sized equipment also decreases operation and maintenance costs. An oversized HVAC equipment function at shorter periods while the undersized are required to run longer to meet the much-needed load. Both are not economical. Accurate air-conditioner sizes regulate humidity better, minimizing growth of molds and thus maintaining a healthy environment. Usually, oversized air conditioners perform lesser dehumidification due to shorter cycling.
Furthermore, HVAC sizing decreases callbacks. Yet the need for conducting HVAC sizing can either be by choice or by circumstance. There are, in fact, some states in America such as California that require load calculations. Whatever is the case, whether you have an option or not, it’s always preferred to calculate the sizes of your HVAC equipment.
The principles and the applications of accurate HVAC sizing are based on ACCA’s (Air-conditioning Contractors of America) guidelines for measuring HVAC sizes of equipment. This manual called ACCA Manual J Residential Load Calculation allows contractors and owners alike to correctly approximate the loading capacities of their heating and air-conditioning systems. A building’s heat loss can be calculated through its air infiltration on doors and windows, leaky ducts, as well as ceilings and walls. Another source for load calculation is the facility’s design condition.
It is imperative, however, that load calculation should be done per room for proper ductwork sizing. Measurements of air infiltration should be approximated, or you may perform a blower-door test. This test can actually give a more accurate calculation of HVAC sizes and should be conducted in retrofit applications. Infiltec.com provides the most comprehensive procedures and tips in conducting the blower-door test. Though this examination will often result to a higher design cost, you are assured of accurate HVAC size calculations. Most of all, it costs more to maintain oversize HVAC equipment in your building.
It is relatively easy to follow the guidelines set by manual J. House plans are ideal sources of information that are practically used in sizing load calculations of the cooling systems installed in new houses. You can also get other valuable details in window type, glazing, house’s orientation, solar gain, and shading from building overhangs.
If you are a contractor or a builder, there are some things you must always remember when you’re sizing HVAC equipment:
- As much as possible, don’t rely on the “rule of thumb.” This system may work, but you can never be assured of its efficiency.
- You might not be bothered by those almost-inaudible roars of air conditioners. This may just be a common scenario. But what you don’t know, these units may not be appropriate for the cooling load—they are simply oversized. To prevent taking unnecessary risks and damages, follow the rules stated in the manual. For sure, it’s safer that way.