Modular Construction HVAC
Proper Zoning
HVAC Design
Proper HVAC Zoning
An important part of air conditioning system design is zoning. No one likes hot and cold calls. Fortunately, with careful design and with equipment in good working order, they can usually be avoided.
The Role of a Thermostat
We should begin by discussing thermostats. Air conditioning systems think that they have only one job. And that job is to keep the thermostat satisfied. It's not to keep occupants comfortable or to keep the space at a reasonable temperature. It heats or cools until the thermostat reaches its setpoint temperature, and then it stops. But most air conditioning systems serve more than one room, how do you keep them all at a comfortable temperature?
Imagine a scenario with several identical rooms: the same walls, windows, and exterior exposures; the same lighting, the same number of people, the same number of computers. If all rooms are the same size and have the same amount of heat-generating equipment, they should heat up at the same rate. And if they are heating up at the same rate, it shouldn't matter which room the thermostat is in, because what is happening in one room, is also happening in the other. See the drawing with offices 9, 10, 11, and 12 below.
If one side of a building (the west side, for example) is all offices with similar equipment, you would expect their heating and cooling patterns to be similar as well. As long as the designer does the calculations to make sure the airflow is proportional to the heating and cooling requirements, it won't matter which room gets the thermostat.
Proportional Loads
Let's look at a second scenario where one room is bigger than another, has more lights, computers, and so on. If the loads of both spaces are proportional to each other, they will heat up at the same rate, even though the room dimensions may vary. The required cooling of these rooms should also be proportional as well, a room that is nearly twice as big and has twice as much load will require nearly double the cooling CFM, see Office 2 and Office 3.
Unique Loading Patterns
Not all rooms have the same loading patterns, however. In an elementary school, for example, the heating requirements in the cafeteria will follow a very different pattern than the classrooms; when the cafeteria is full, the classrooms will be empty. A conference room will have a different heating and cooling profile than offices. Rooms on the east side of the building will need heating and cooling at different times than rooms on the west side. When possible, parts of the building with unique load patterns and profiles should be given their own system.
Do All Rooms with Unique Loads require Dedicated Systems?
No. Not every room with unique heating and cooling patterns needs its own system. Take a break room or janitor's room for example. Heating and cooling requirements in these rooms will follow different patterns than the rest of the building. They may be empty in the morning, very busy at noon, and empty the rest of the day, or only in use briefly after hours. But these rooms are small, and people are not in them for very long. Restrooms and small conference rooms are similar, and the added cost of individual temperature control for these rooms may not be worth it.
Large Rooms (such as training rooms and classrooms)
However, large training rooms, classrooms, and other rooms where large numbers of people will be for long times are good candidates for dedicated heating and cooling systems.
If you'd like help thinking through a complex zoning situation, feel free to email me at jamescrockettpe@gmail.com, or call me at (385) 276-4669.