Industry Standard for Thermostat Verification

[jason21psu]

Does anyone know if there is some type of industry standard for verifying the accuracy of DDC thermostats and humidistats? I am mostly looking for recommendations on frequency of testing and methods for testing based on type of space being controlled or monitored.

Thanks in advance for any help.
Jason

[Cagey57]

Need more specific "Industry Segment". Pharmacutical has very specfic testing criteria with NIST calibrated (traceable) test equipment, USDA is similar. Don't go there unless you have to.

What are you working on, office buildings, Walk-in collers/freezers, Telco/Data rooms, Manufacturing etc. ?

We get asked to "check" sensors and transmitters a couple times a year but that's for comm. office space. We use test equipment that is more accurate as the device we are testing. For Humidity, if the transmitter is +/- 3% Rh we test with +/- 2%. On DDC sensors I use my Fluke 52. One thing that we have had issues with is operators using IR thermometers and telling use the DDC sensors are "way off". Once we get them to read the instructions they stop telling us that.

As far as frequency of testing and calibration, it all depends on the application. Once a year on a PM basis is almost overkill but it finds a few bad ones.

[jason21psu]

I guess I am looking for information based on the industry segment. Generally these are museum spaces where the goal is to maintain temperature between 68°F and 72°F and RH between 45% and 55%. But there are also spaces which more resemble office space. I was hoping ASHRAE had something published with recommendations but I have not been able to find anything as of yet.

In this day and age data showing energy savings (both $ and carbon emissions saved) by having an accurate stats would be great.

The other part of my question was the method used for testing. We have had situations where the stat was mounted on an interior wall and a draft was being induced through that wall, throwing the sensor reading off. Is there a standard method for testing that would address this issue and others that could cause an accurate stat to not read space conditions accurately.

Thanks for the help!

[Cagey57]

Ah ha ! A museum. We did a museum, the curator wanted similar conditions. The temp was no problem Rh however was another matter.

Seal all of your wall sensor boxes to stop the infiltration or put foam isolaters under the back plates. Unless you have air locks or excellent door seals your Rh will have to be controlled to satisfy the exibit and archive areas, everwhere else will have to deal with what they get. Remember, the Museum's items/artifacts are the "Occupant" of the building not the people.

See if you can get your hands on a Visala temp/Rh meter (very nice, rather expensive, you could buy 3 Fluke 87's for what they cost).You can get the Visala NIST traceable calibrated. We did some pharmacutical Validation and the FDA accepted the Visala for that so they MUST be good ! That will exceed the accuracy of almost any temp/Rh sensor you have in the place.

Sounds like you are finding problems with the "Building/space envelope". Plug the holes before you fill the bucket

I saw something to this effect on someones signature on the boards "You have to control the environment before you can condition it". Sounds like it applies in your situation.

[joekent]

Worked with Visala and they are very good as we were maintaining ECGs. However one of the simplest forms to check them for accuracy is a psycrommeter. Old school yes. But call me old fashioned I still believe fire is magic.

[Cagey57]

You mean fire isn't magic ?:confused:
No arguemnet on the sling psych. The problem I run into is non-technical people have problems believeing me when I pull out the psych chart. A digital display is hard to argue with and easier to read.

[sysint]

I guess I am looking for information based on the industry segment. Generally these are museum spaces where the goal is to maintain temperature between 68°F and 72°F and RH between 45% and 55%. But there are also spaces which more resemble office space. I was hoping ASHRAE had something published with recommendations but I have not been able to find anything as of yet.

In this day and age data showing energy savings (both $ and carbon emissions saved) by having an accurate stats would be great.

The other part of my question was the method used for testing. We have had situations where the stat was mounted on an interior wall and a draft was being induced through that wall, throwing the sensor reading off. Is there a standard method for testing that would address this issue and others that could cause an accurate stat to not read space conditions accurately.

Thanks for the help! I think you can make an argument it is not necessarily the accuracy of the stat but how the controller actually operates and what type of system is being utilized. Lets say your sensor is .5 degrees off. Does that matter when you allow a 4F swing in temperature? I think you setup the controller for 3.5F +/- .5 and you have the same result.

[simsd]

Like sysint said, the equipment can be one of your real issues. If the sensors are accurate but the equipment is not, then you may have a problem. As an example, if you are trying to control humidity (which can be difficult) if your humidifier is over sized, it might spray too much steam in the duct as it tries to humidify (just one example).

[printer2]

I used to calibrate our humidity meters in an environmental chamber when I was working for a local aerospace firm. When I was a student I built an environmental chamber that controlled temperature and humidity. It was the size of a small microwave oven, made of insulating foam skinned with kitchen laminate, had two controllers one for humidity one for temperature.

Proportional control for power to the heating elements and thermoelectric coolers and humidity was pulsed on and off. In such a small space adding a small amount of moisture was problematic. Solved the problem by using an air pump from a fish tank and bubbling it through a container with water. I could easily control the humidity in 5% intervals.

Get a humidity sensor calibrated and away you go. Other than the controllers which I borrowed it cost me $35. Tossed it out because I had no other purpose for it, years later when I did some teaching I thought it would have made a good trainer for some lessons.

[printer2]

As simsd said controlling humidity can be challenging. I have a bit of a problem with our hospital's operating rooms because of how the HVAC system was designed. The sensor is in the return air duct and there is a big lag in the control.

When the doctors change the humidity level it can dump steam into the supply duct and it looks like we are putting on a rock show. I slowed things down, some doctors do not understand why they have to set the controls beforehand for what they want but others realize sometimes you have to work with what you got.

[jason21psu]

I appreciate everyone who has taken the time to respond to my post but the crux of my issue is that I need to field verify the accuracy of the stats. Aside from the performance of the HVAC system, because these are artifact storage or exhibit areas, the zone conditions measured at the stats are used for accreditation purposes.

We have a web-enabled BACnet controlled system that takes care of the logging and archiving of the data. We do have other devices used to monitor the spaces but we are trying to move away from that because it requires human interaction to get the data from them. There are many other disadvantages like cost and not being able to access the data real time that are precipitating the desire to rely on the stats for both the control and accreditation of the spaces.

So like I said earlier what I am really looking for is a guideline, published by an industry authority like ASHRAE, that gives recommendations for stat accuracy verification methods. I am aware that manufacturers have recommendations for how often their stats should be calibrated/verified but again that is not the information I am looking for. If the answer to my question is that such a document does not exists then that is an acceptable answer but I need to exhaust all possibilities when looking for this information.

Thanks again!

Jason

[simsd]

I'm not sure there would be any "Official" document other than the one from the manufacturer. So I'm going to go out on a limb here and say that there is no official one (anyone, please correct me if I'm wrong).

That being said, how are you going to do the verification/calibration in the future? What you really might want to make sure of, is that the reference device (thermometer or whatever instrument that you are using) is calibrated annually to some sort of national accreditation (like NIST) so that at least when you compare the rooms, you are comparing them to something that itself has not gone out of whack.

[Cagey57]

Spent an hour trying to find a definitive ASHRAE reference, came up empty, I may have been looking in the wrong places.

The Authority that give's the "Accreditation" you refer to should either have or provide a guideline for said "accreditation" ranges. Lacking that I suspect your best bet would be to create your own "Monitoring and Verification Plan" with the museum staff's help and then implement it. Unless you have NIST traceable sensors in place your "Plan" will far exceed any accreditation requirements and also allow you to identify any control/equipment problems that need attention.

Start with an initial survey and record Everything, then next month, 60 days, 90 dayswhatever, re-check and calibrate/adjust as needed to meet your plan.

You will probably identify needed work in doing that so make sure your customerunderstand that up front.

[simsd]

"Wait!...explain to me, again, why you think a broken belt is a Controls Problem."

BTW.....Love it!!!

[sysint]

I appreciate everyone who has taken the time to respond to my post but the crux of my issue is that I need to field verify the accuracy of the stats. Accuracy of the temperature sensor in the stat or the control algorithm? Both?


...So like I said earlier what I am really looking for is a guideline, published by an industry authority like ASHRAE, that gives recommendations for stat accuracy verification methods.... I thought you were looking for a quality standard....