Pellissippi State Facilities Department
HVAC (Heating, Ventilation, and Air Conditioning) 101
We receive many calls and requests regarding temperature problems in classrooms and offices. This section is designed to help answer questions regarding how our HVAC (heating, ventilation, and air conditioning) system operates. While this explanation pertains primarily to the Hardin Valley campus, it applies almost equally as well to the branch campuses.
On the Hardin Valley campus, the heating and air conditioning for the major buildings is supplied through a central plant system. We use chilled and hot water, which is generated in the Physical Plant, to cool and heat the buildings. This system is very different from your home systems and does not react the same way to rapid changes in weather or adjustments. One analogy that comes to mind would be to compare driving a small sports car to driving a city transit bus. The sports car, your home system, is quick and agile. The transit bus, our system, requires lots of room, and more time and distance to stop and maneuver.
The central plant system is designed to provide a uniform temperature throughout a building, and maintain it. It was not designed to provide varying temperatures from room to room based on individual preferences. For example, only classrooms and offices on the exterior perimeter of the building have heat. Most rooms in the interior portions of the buildings only have the ability to cool. In addition not all offices or rooms have thermostats. There may be a centrally located thermostat that controls a “zone”. What many times appears to be a thermostat is actually simply a sensor, which relays information back to a central controller.
Our system operates by providing heat and air conditioning simultaneously. Even on the coldest days of the year we are often providing chilled air to central portions of a building, while at the same time providing heat to outer rooms. The open computer lab on the 3rd floor of the ERC is a good example of this. Due to the heat generated by the large number of computers in this area, it requires air conditioning even on the coldest days of the year.
You may also be surprised to know that we actually have to generate heat in the summer. Federal guidelines dictate that we maintain building humidity levels between 30%- 60%. On humid days we sometimes have to place a false heat load in an area to increase the amount of cooling in that same area. Humidity is removed with cool air.
We are also required to provide a minimum of 10% outside fresh air into all of our buildings. Obviously on rainy days this will increase the humidity levels indoors as well. If you come into a classroom slightly damp or even wet from the rain, it will feel much cooler than it really is as the moisture evaporates from your clothes due to the cool air in the room. Even though the room temperature is the same as it was yesterday, today it feels colder since the added evaporation of the moisture from your clothing actually creates more cooling on your body.
The thermostats you see located in the offices and classrooms around campus, were not designed to be continually adjusted to meet individual preferences. Remember that our system was designed to maintain a predetermined uniform temperature throughout the buildings. The thermostats are primarily used as monitors, not controllers. This is why they were designed to only be accessible with a small Allen wrench. They were not intended to be adjusted on a regular basis. Unfortunately most people don't realize this and make adjustments to the thermostat. In many cases when we respond to a complaint regarding room temperature, we find that the thermostat has been changed or even damaged, in an attempt to get it open to adjust the temperature. For this reason we have begun installing an additional lock box over the thermostats. These will eventually be placed on all thermostats in an attempt to reduce the cost of replacing damaged thermostats, and problems of regulating temperatures in rooms.
Keep in mind also that not all rooms and offices have thermostats. Generally a cluster of four offices will be controlled by one thermostat located in one of the offices. Most times this thermostat will control heat only. The thermostat that controls cooling may be located in another office. If you turn up the heat in your office, others may be too warm. They may then turn up the a/c, making you and others too cold. Again, these thermostats were not intended to be continually adjusted, but to act primarily as sensors to maintain a constant temperature in the building.
If a room is not a comfortable temperature, it is most likely a result of a problem with the variable air volume controller in the ceiling, or a leak in the pneumatic line that operates the thermostat. These are items that can be easily corrected if we are made aware of the problem. Too often we only find out there is a problem after people have been putting up with it for a long time. Please call the Physical Plant any time there is a problem with room temperature.
We often get questions regarding Indoor Air Quality, particularly concerns about mold. Our air handling systems are treated to prevent mold growth within the systems, and filters are changed on a regular schedule to prevent dust accumulation within the ductwork. The college's internal auditor makes periodic inspections to assure that proper preventive maintenance is maintained on these systems.
If you have concerns or questions regarding Indoor Air Quality, don't hesitate to call the Facilities office. We'll be glad to take a look at your area of concern and make any corrections necessary to assure that we are providing a healthy atmosphere for all faculty, students and staff.
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