Pneumatic Controller(s)

[qburt]

I am looking for a SINGLE control for pneumatics that can be remotely adjust from 45 - 120 degrees f and be able to have a manually set low limit set point.
Righ now my only known alternative is to use 2 controllers and a remote variable switch in the panel door to adjust the temp.
Is ther somthing out on the market that has 2 set points? (one for low limit one for high limit) that can use a variable pneumatic remote controller?

[ozone drone]

All pneumatic control manufacturers make a dual input receiver controller. Say you want to control discharge air temperature. One sensor monitors discharge air temp and the second sensor monitors whatever you want to reset the discharge air temp....examples
1. return air temperature
2. outside air temperature
3. room air temperature

Set up a reset schedule such as


Room temp 72 deg Discharge air 60 deg
Room temp 68 deg Discharge air 80 deg

[qburt]

Well I have an air handler that goes to some meeting rooms. the A/H itself was designed to put out @ 45 - 55 deg f air all year. The reheat coils at the rooms would add any needed warmth but are no longer in use so we just jocky the crap out of the A/H all of the time.
The A/H has only a pre-heat coil and a cooling coil (no re-heat in the A/H). and we don't run the chiller in the winter so we rely on outside air to cool the place so I can't let the reheat coil get below 35 deg.
I would like to replace all of the out-dated controls with one if possible but it would need to be able to remotely adjust from @ 45 to maybe 120 deg f (depending on the function and # of people).
I am generally a Honeywell fan but am not able to find anything fitting my need unless I pair up 2 controllers.

[hvac3901]

the details help alot.
how many meeting rooms?

the problem i see is you have several loads, and one source of heating or cooling for all as i'm sure you know. is there some manner of zone control? or are the rooms constant volume? i'm guessing that from your post it is safe to infer you are looking to control from a single sensor/set point adjustment. keep in mind even though you are allowing the occupants control over their own destiny by remote set-point adjustment it is not going to be an atuomatic control responce due to the location of the duct sensor and its relation to the load it serves.

so i would propose you just stage the valve spring ranges and and run them from a t-stat output, easier, cheaper, and better still automatic. who dos'nt like that?

hell if you want more than one t-stat dump the t-stat outputs into a high-low selector relay or an averaging relay. and take care of multiple zones with the same unit. (to some degree)

i know jhonson has integral remote set-point adjustment pipe connections, but i hate calibrating those damn things.

you have alot of options but the best and obvious is to repair the rehat coils. trying to properly control half operable systems is a lost cause.

[flange]

use a dual input control with a manual potentiometer for cpa. though this wont solve your problems, only mask them.

[DeltaT]

Originally posted by qburt
Well I have an air handler that goes to some meeting rooms. the A/H itself was designed to put out @ 45 - 55 deg f air all year. The reheat coils at the rooms would add any needed warmth but are no longer in use so we just jocky the crap out of the A/H all of the time.
The A/H has only a pre-heat coil and a cooling coil (no re-heat in the A/H). and we don't run the chiller in the winter so we rely on outside air to cool the place so I can't let the reheat coil get below 35 deg.
I would like to replace all of the out-dated controls with one if possible but it would need to be able to remotely adjust from @ 45 to maybe 120 deg f (depending on the function and # of people).
I am generally a Honeywell fan but am not able to find anything fitting my need unless I pair up 2 controllers.

I bet the original controls and control sequence is just fine. Some of your comments on control are probably not correct or your assumption is not correct. For instance, the A/H will not put out 45-55 deg all year around simply bacause you are not running the chiller.

During heating sequence I just bet he something in the A/H or controls add heat to the supply air. You must add heat during the heating season.

As for individual meeting room temp control, you should have individual room sensors controlling the zone or A/H to maintain the set point of the room temp. If the room is too hot due to a high heat load such as lots of people in the meeting room, then mechanical refrigeration is probably going to be necessary.

If you have only one A/H for many meeting rooms then the A/H controls can provide some cooler air but that would most likely not be an adequate cooling source for a room full of people as humidity from the outside getting introduced into a room full of a heat load already giving off lots of humidity and heat will only cause more discomfort.

The reheat coil and it's controls are there mainly for safety and somewhat a guarantee to maintain some sort of A/H discharge temperature control. Those reheat control are a seperate issue as well as the individual zone controllers.

[sysint]

Qburt-
Since you have such a modified system you have to analyze what the original intent was and work from there.

Is this a CV reheat system? Why were the reheat coils disconnected? Sounds like it could be a decent system that's crap now. Economizer? How big is this unit? How big is the building?

Also, for the cost of pneumatics nowadays, you can get alot of electronic. Aggregate the stat signal and get a transducer to transfer the value to the AHU controller and slowly go through and retrofit.

Are you renting or do you own it?

[Control Man]

Had a installation like that , they BLEW the reheat coils and never repaired them and wanted the system to operate the way it was originally designed.

[qburt]

To answer some of the questions as to why it is the way it is ...
The building is a hotel and it is a large one.
Although it would be best ot repair things and get it back to its original design, it is the cost factor that keeps it from happening.
The reheat coil was only to keep the chilled coils from freezing and the economizer is there to limit the need for the chiller to run at 100%. The chiller was designed for year round since the area it serves could be loaded greatly with a lot of people and equipment.
The reheat coils were there to bring the individual temps up via wall-stats that have also been removed.
The 3 individual rooms can open up into one L A R G E ballroom which is only half of the lower level. The other (smaller) half is in need of the same tweaking so this is why I want to do this with the least amount of controls as possible. The more I save the hotel ... the better I look.
The original layout of the building was outstanding and was the cadillac of its day in the late 60's and early 70's.
I guess I need to keep trying to get the money to rebuild this puppy back up right.

[DeltaT]

qburt
The only way to have proper temperature control of your 3 rooms or one large room is to return the control system to it's original configuration using pneumatic, electric or electronic controls.

Sounds like most of your needs will be for creature comfort as the rooms are used, individually or all. This means the proper amount of refrigerated air to the individual room(s) as needed and as sensed by the individual room sensor.

Even in the winter if your room(s) have too much heat load through occupancy, you will need to have the chiller on to supply refrigerated air...period. The economizer, which I bet is not working, will provide cold, humid air most of the time down to a certain temperature point. At that temperature the economizer must close down to protect coils from freezing.

So you are right back to requirement for refrigerated air again. Get back to basic control theory and you will maintain control. Any other way will not give you even temperature control of your room(s).

I've done a lot of work for hotels and find most of them cheap so I can relate. They prefer flowers in the lobby to operating systems, including the kitchen refrigeration.

Good luck

[hvac3901]

No controls= no control

You will not look good when the customer has spent any money to operate a system with minimal controls and all the demands of, as if they spent thousands on state of the art equipment. IMO they are generally ignorant to what we do and do not understand that putting money in our pocket does not solve all of their problems.

i still clain the minimum is what i said, but i won't be there to be on the call back. t-stats, valve corelation, hi low selector relay, and thats it. aside from the labor to install the tubing. thats as easy and as cheap as it gets and it will operate the same. but it is better than nothing if thats how your looking at it.

No a question for QBERT if the reheat coils exsist to stop the coils from freezing and they are no longer in service then what prevents it now? please tell, i would like to understand this. CHW coils freezing? I'm probably missing something here.

[Edited by hvac3901 on 02-03-2005 at 10:00 PM]