Air Temp Measurement

[dwyndell]

We have expanded our 400 seat auditorium to add an additional 200 seats (600 seats total). The expansion came with two additional HVAC units independently controlled by two additional thermostats. This appears to be a very poorly designed system. Our existing unit measured the return air temperature. The new units measure the temperature at the controls on the wall. Is there a code that states when return air temperature should be measured and when measuring on the wall is acceptable?

Thanks

 

[DRWeig]

Dwyndell,

No code governs thermostat placement in such an application, just engineering judgement. Auditoriums are tough to begin with, in terms of air distribution. With three independent units, you really need an automation system coordinating their efforts, with some combination of return air and space temperature sensing points.

Good luck to you, let us know what you come up with for a solution!

Good on ya,

Goober Dave

 

[DRWeig]

Just a notice -- this is cross-posted in the ASHRAE forum too.

Goober Dave

 

[IRstuff]

Ultimately, it almost doesn't really matter where the sensors are. The system's performance will be calibrated by how many complaints you get for the temperature being too high or too low. Obviously, the sensors should be spatially disparate, to ensure a wider sample of temperatures.

Ideally, you should also have humidity sensors, since the biggest perturbations in the system are the heat load and perspiration/respiration of the people in the auditorium.

Adequate mixing is essential for comfort. Residential A/C winds up with 55°F air directly under the vent, and 80° along the hottest wall.

TTFN

FAQ731-376

 

[Aircool]

When you say the system appears to be poorly designed, what problems are you experiencing?
Are the areas being overcooled/overheated or does the temperature cycle?
If it is constantly too hot or too cold then the sensors (I presume they are sensors and not thermostats) could be in a position that is not indicative of the area overall, however if the space conditions cycle between hot and cold then the system may well have not been commissioned correctly.
Other things to look out for, are the sensors positioned near something that gives off heat for example?

 

[jcacman]

I would go beyond the humidity sensors and say that the most comfortable auditoriums have C02 sensors and can modulate the OSA. it is also a huge energy savings only introducing the OSA that is needed. An automation system is definitely the way to go and the savings that could be achieved would definitely justify the cost. There are many options many that are very simple in both design and implimentation. with 3 different units operating independently sensor location is really irrelevant. The space needs to operate as one system

 

[sridhar1312]

It appears the units are not located in the same room. Thus the supply air from the units added to take the additional load seems to be separate from main existing unit.
Even if the units are apart as long as the air side is connected then equal distribution can be ensured to maintain the space conditions.
Thermostat shall be located in such a way where it can sense average room temperature.That will ensure the room conditions are well maintained.
However it depends on the Air distribution system which is the key aspect. If air distribution is not proper then also conditions will not come.