HVAC Thermostat for Calibration Laboratory

[SGCalLab]

I manage an internal calibration lab inside a climate controlled factory.

The lab is in a 20 x 24 room with restricted access. We have a fairly new Trane 3 Ton HVAC (designed for home use) just for our room along with a Honeywell thermostat (home use).

We try to maintain 20-21 C. But the temp will fluctuate up to 22-23 C multiple times during the day.

I feel the issue may be with the thermostat.

Can anyone recommend a more accurate, stable thermostat possibly designed for this type of situation? It's tough to search for something like that.

 

[richep]

We have the same problem. I have been thinking about a thermostat change myself.

 

[Marc]

If the room is insulated well you would find it more stable.

When I was in aerospace electronics years ago our inside calibration lab had an air lock like entry, and entering and leaving frequently was discouraged. Only certain people were allowed entry. Temperature was stable +/- 1ºF if I remember correctly. The room was highly insulated, as you might guess.

So, the first thing is - How well insulated (which includes sealed) is the room?

As to the thermostat, I would talk to Honeywell about available compatible thermostats. I know from working in a greenhouse on work-study in college there are a wide range of thermostats. Some have a very wide range - E.g.: Turn on at 80º and stay on until 70º.

I would think that 20º to 21º is a relatively tight range.

NOTE: Obviously this isn't my specialty by any means...

I think the next thing that comes into play is the humidity. A few thoughts: How does Humidity Affect Air Conditioning and Heating

I assume it is an "always on" fan. One of the things I look for when installing a new AC unit in a property these days is one on which the fan runs continuously. Many units have variable speed fans, as well. Where I am at now the fan runs continuously, and if you open a door after a few minutes you can hear the fan speed increase as it tries to compensate. Close the door and in a few minutes the fan speed slowly decreases until it is back to its temperature set point.

HVAC is a specialty - You might want to contact a specialist for some insight.

Food for thought: Thermostat Adjustable Tolerance - HVAC - DIY Chatroom Home Improvement Forum

 

[BradM]

Hello there!

I realize this is horribly basic...
Why not just turn down the thermostat to maintain the temperature you're looking for? Then you're not out any money.

 

[SGCalLab]

Thanks Brad! One big reason is that this area is both the lab and the admin area and keeping it around 18C would be very cold to work in. 20 is already quite chilly, I guess we are all thin blooded!

The thermometer we have has a built in 3 degree swing. I have heard there are some out there that go down to .5, but I am having trouble finding one.

 

[SGCalLab]

The walls are some kind of pre-engineered walls that they built the lab inside the factory for us to have a place to work.

The factory is also air conditioned, probably about 3-4 degrees warmer than the lab on average.

 

[Marc]

<snip> I have heard there are some out there that go down to .5, but I am having trouble finding one.

There are but they're expensive and may not even work (or work properly) with your system.

 

[dwperron]

Trane makes a thermostat that might fit your needs, a model X13511538-01.
You can see the manual at:

http://www.trane.com/content/dam/Tr...ats/prog/documents/BAS-SVX44A-EN_07282011.pdf

This has 0.1° resolution and can be set for a 1°C deadband and for temperature cycle control based on load.

 

[dgriffith]

I manage an internal calibration lab inside a climate controlled factory.

The lab is in a 20 x 24 room with restricted access. We have a fairly new Trane 3 Ton HVAC (designed for home use) just for our room along with a Honeywell thermostat (home use).

We try to maintain 20-21 C. But the temp will fluctuate up to 22-23 C multiple times during the day.

I feel the issue may be with the thermostat.

Can anyone recommend a more accurate, stable thermostat possibly designed for this type of situation? It's tough to search for something like that.

You don't say what kind of work is done in the lab. Do you have windows and or do you have an outside wall? Where is the thermostat located? The temperature might fluctuate but how quickly? And how badly does the temperature affect your process if it changes by 2 °C in 30 minutes? In 2 hours?
A controller with a PID function and multiple zone sampling would give you a pretty good controller for an average set point temperature.
In the end, I think, do you need the temperature to be stable for long periods, or do you just need to know what the temperature is at any point in time?