Have you ever walked into an office building and seen electric heaters on the floor by people’s desks? Even worse, have you walked by an office and noticed cloth or cardboard stuffed into the diffuser? That’s a clear indication of comfort problems. A person is thermally comfortable when their bodies heat loss equals their heat production. People vary, so what is comfortable for one individual is not for another. What’s the solution? Oftentimes a contractor will recommend installing airflow dampers in or rerouting ductwork. More times than not, this results in an unsatisfactory solution. How else can you correct the problem? One way is with a VAV diffuser.
What is that you ask? Simply put, a VAV (variable air volume) diffuser is one which modifies airflow to the space based on a thermostat controlled by the user. In other words, in a space heated and cooled by a rooftop unit, individual offices or spaces can have their own diffuser and their own thermostat. If more than one third of the load is controlled by these diffusers however, a dump zone must be maintained in order to avoid damage to the compressor. So for example, on a 5 ton unit, (2000 CFM) a dump zone must be maintained if more than 600 CFM is being controlled by VAV diffusers. How do they work?
Using an architectural Square plaque ceiling diffuser, manufacturers incorporate a wax filled thermal element attached to the top side of the plaque. (See picture) There are no wires involved. This thermal element gets its room air temperature reading via a sensor mounted in the center of the diffuser. The sensor allows for no more than a 1°F dead band between the induced room air temperature measured by the sensor and that of the zone air being supplied to the diffuser. If the space begins to heat up in the cooling mode, wax in the thermal element also begins to heat up, thereby raising up the damper in the diffuser and allowing more airflow into the space. As the room sensor become satisfied, the wax in the thermal element begins to cool down and the actuator assembly lowers, thereby reducing airflow to the space. At least one manufacturers design allows the user to adjust the minimum airflow of a satisfied diffuser anywhere between 0-30%. This capability allows the control necessary to meet Ashrae Standard 62. Furthermore, these diffusers are listed by AHRI, so their rated performance has been tested by a certified lab.
What does this mean for the astute contractor? Simply put, opportunity! Consider the following statistics.
- Thermal comfort is the most often cited complaint in office buildings today
- Studies have linked improved comfort to reduced absenteeism, and thereby improved productivity
- Labor costs are typically 10 times that of a property, so an improvement in comfort is rewarded with large returns in productivity
In a commercial building setting, awareness of the technologies that have a measurable impact on personal comfort and therefore productivity can help your company become the contractor of choice for problematic applications.
Picture courtesy of Titus