There are many factors to consider when sizing HVAC systems in commercial buildings. The most important rule of thumb is to size the HVAC unit based on the load it needs to cool or heat per hour. For example, if you have a large office building that is mostly empty, you will need larger HVAC systems than a constantly full building with very little space.
Current variables for sizing commercial buildings include the following:
1. Wall Height per Story in the Building
High ceilings require more airflow, whereas lower ceilings do not need as much airflow to feel comfortable. You need to install one ton of HVAC for every 300 square feet of uplift (the number of cubic feet added to the volume by high ceilings).
2. Active Hours
The active hour is the number of hours in each 24-hour day that a property requires cooling or heating. Some buildings are occupied 12 to 14 hours per day, whereas others may be occupied for only 8 to 10 hours per day.
Larger buildings with fewer occupants will require larger HVAC systems than smaller buildings with the same number.
3. Number of People in Each Building
Office buildings and other commercial properties will need more HVAC units based on the number of people using them daily (if they are open for business). A ticketing office such as an airline or train station, which is only occupied during certain times of the day, will need fewer HVAC units than that same building used as an office building.
4. Number of Floors in Each Building
The number of floors in a building will determine how difficult it is to cool or heat the air. A one-story structure, such as a factory with offices on top, may require fewer HVAC units than a ten-story office building.
Based on the number of floors and the design hours, you can use this formula to estimate the load on your HVAC system for a specific building:
Roof Area x Design Hours ÷ 2000 = Building Load in Btu/hr.
5. Square Footage of Each Building
The size of individual space that the HVAC system needs to cool or heat will dictate what CFM (cubic feet per minute) you require for each duct in each room. If the heating and cooling equipment has more than one speed, then multiple speeds can be used.
This means if a room is 3,000 square feet and has a ceiling height of 12 feet with a door opening at 8 feet, you can use this formula to determine the CFM needed:
3,000 x 12 ÷ 8 = 100 CFM
Additional variables for cooling a commercial space include the following:
Temperature Difference Between Indoor and Outdoor
The temperature difference between the inside and the outdoors will dictate how much airflow is needed. When it is colder outdoors, more indoor heating will be required to bring in the air to maintain a comfortable environment in your building.
When it is warmer outside, the reverse is true – you will need more cooling indoors to maintain a comfortable temperature.
Wind Speed Around the Building
Strong wind gusts can result in increased airflow requirements simply for your HVAC system to keep up with the pressure changes created by the wind. This will require more airflow, especially if you do not have enough space between buildings or other obstacles to allow the wind to flow through your building.
Wind Direction Around the Building
Wind coming from one direction will require different airflow requirements than coming from a completely different direction.
For example, an office building with its air intakes on one side and exhausts on the other side will need less airflow overall than that same office building if the intakes and exhausts were on the same side. This is because half of the HVAC units would not be working as hard to provide cooling or heating at one time.
Ambient Temperature
The indoor air temperature will dictate how much additional heat needs to be added during winter and how much additional cooling you need to provide during summer. For example, if the outside air is 100 degrees Fahrenheit, you will need less cooling inside to maintain a comfortable environment than that same office building would need on an 80-degree day.
Outdoor Humidity
The higher the humidity in your outdoor air, the more moisture needs to be added inside through your air conditioning to keep the relative humidity at a comfortable level. This means more cooling equipment will be needed to maintain a comfortable temperature.
Building’s Occupancy/Building’s Use
How many people are going to be occupying the space at any given point in time? If a building is not occupied, how long it can go between uses will determine how much energy your HVAC system uses when not in use.
You need to install the equipment that you need to meet the needs of your business while not in use, especially if it is an area where access isn’t needed. This will depend on how often the building gets used and for what purpose it gets used.
Air Filtration Required
Some facilities are better suited for air filtering than others, such as those with high amounts of dust and debris outdoors since they could easily pollute the inside air. This is especially important for indoor environments. It would help if you filtered out allergens and other small particles that can cause problems for your employees and tenants in the commercial building.
An HVAC system for 1,000 square feet would require 100 CFM at maximum. For this example, the recommended size is a 3-ton unit which covers up to 720 square feet. The remaining 280 square feet can be covered by two 2-ton units, which makes your space comfortable even when only one unit is in use.
Call Hanover Supply Company to Install HVAC Units in Your Commercial Building
We supply and install HVAC units to keep your commercial space comfortable all year long. Reach out to Hanover Supply Company today to schedule a consultation with one of our knowledgeable representatives. Call #973-887-9196.