25 Ton AAON unit - space is too hot

[beenthere]

AAon made that unit for that building/space based on what the original area use was. When you call Aaon tech support. They can tell you how it was originally set up, along with whether or not its suppose to have return air, and if it can use supply air temp sensing. You may also have a building pressure sensor.

[icy78]

AAon made that unit for that building/space based on what the original area use was. When you call Aaon tech support. They can tell you how it was originally set up, along with whether or not its suppose to have return air, and if it can use supply air temp sensing. You may also have a building pressure sensor.

Yes that is true. And a good point. I would suggest though that you call wattmaster and not Aaon because wattmaster will know more about their controls, at least that's been my experience. Also if you look on the name tag of the interior of the door it will probably list as MUAU-1 etc.

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[Dan_G]

I'll be going back in the next week or two. I spoke to Wattmaster tech support. They said this was configured as a MUA. They also said I can add the indoor temperature sensor and the system will control the space temperature much better. They gave me the part number for the indoor temperature sensor and told me what terminals are used to wire it in. So I can get that squared away without any problems (so long as we can get the wire run). I certainly did not get all the details I need. So I'll be calling them again when we install the indoor temp sensor.

[71CHOPS]

It sounds like you’re in a bit over your head...and I mean no offense saying that.

You’ve found the drawings (design) for the space. Now you are being asked to change the original unit design to fit a new configuration of the space. How much liability for design of the entire hvac system are you willing to accept? What if the changes you make don’t produce the promised results?

Aaon support should have told you that the change in unit design will be reviewed by engineering, then a price would be given for selling you the sensor AND for changing the factory design data sheets.

If you weren’t told about that, I would question the reps you’re dealing with. Are you taking to Aaon factory support, or a local Aaon sales rep?

[DeltaT]

"So basically, the machine was never designed to function as a heater or an air conditioner. It just does what it does and the temperature in the space is completely out of control – boiling hot, freezing cold … whatever the machine decides to do, that’s what you get. But this machine serves a cafeteria. They don't need a make-up air unit - they just need to control the temperature in the space like every other room in the building."

Your statement is not necessarily true. Especially in schools, gyms & in any wide open area where people will be & that has equal exhaust fans most of the time a massive amount of fresh air is required. But that air can not be cold so that system controls the discharge air going into the room based on the calculated load that the room may need. If there is no air conditioning for that room them the only thing these units can do is to keep the air fresh but not let the room get cold. If there is the option of A/C then an outside temperature sensor will allow the system to switch over to cooling. Not many control humidity but that is also another option. In all cased the controls should be readily accessible to the maintenance/operators. Every public school in every state has these types of systems that I know of. They are typical & standard for industry standards for health & odor reasons.

[Dan_G]

It sounds like you’re in a bit over your head...and I mean no offense saying that.

You’ve found the drawings (design) for the space. Now you are being asked to change the original unit design to fit a new configuration of the space. How much liability for design of the entire hvac system are you willing to accept? What if the changes you make don’t produce the promised results?

Aaon support should have told you that the change in unit design will be reviewed by engineering, then a price would be given for selling you the sensor AND for changing the factory design data sheets.

If you weren’t told about that, I would question the reps you’re dealing with. Are you taking to Aaon factory support, or a local Aaon sales rep?

This is all correct, I’m definitely in a bit over my head. I’m not sure why Orion/Wattmaster tech support never suggested that this change should be reviewed by engineering. In the end, my way of dealing with this was to tell my boss about all of my concerns and also drag our most senior tech/field supervisor into the project. I can’t really do more than that. My boss and the customer knows that this has some risk to it. We do a ton of work for this customer. I know they are happy with us. If this project does not work to the customer’s satisfaction, I’m sure we will have to take it to the next level.

[beenthere]

This is all correct, I’m definitely in a bit over my head.

I’m not sure why Orion/Wattmaster tech support never suggested that this change should be reviewed by engineering.

Cause you didn't volunteer to pay for it.

In the end, my way of dealing with this was to tell my boss about all of my concerns and also drag our most senior tech/field supervisor into the project. I can’t really do more than that. My boss and the customer knows that this has some risk to it. We do a ton of work for this customer. I know they are happy with us. If this project does not work to the customer’s satisfaction, I’m sure we will have to take it to the next level.

While Aaon owns Wattmaster. You spoke to a Wattmaster rep, not an Aaon tech support person. So Wattmaster isn't going to suggest an Aaon engineer review anything. An Aaon tech support person might have though. Which is why you should have called Aaon tech support instead.

Wattmaster,knows their controls, Aaon knows their unit.

[icy78]

This is all correct, I’m definitely in a bit over my head. I’m not sure why Orion/Wattmaster tech support never suggested that this change should be reviewed by engineering. In the end, my way of dealing with this was to tell my boss about all of my concerns and also drag our most senior tech/field supervisor into the project. I can’t really do more than that. My boss and the customer knows that this has some risk to it. We do a ton of work for this customer. I know they are happy with us. If this project does not work to the customer’s satisfaction, I’m sure we will have to take it to the next level.

@71CHOPS
Adding a space sensor is simple and doesnt need engineering approval from Aaon or wattmaster. Sometimes they'll give you another schematic tho.
But you're right that it should really go thru those guys ,as they will think of things that we wouldnt.)


@Dan_G
Wattmaster controls will walk you thru config changes you can make, with them on-line. Or you can download Prism, and buy the service tool and connect them thru Teamviewer and have them do it all for you. (Takes the fun out of it tho!)
Using the space sensor allows you a reset source so you can supply cooler air or warmer air as needed, while still using it as a MUA.
As I said before, look into the conventional mode too. (With return ducting) It will then use the space sensor as control point and heat/cool/blower cycle, based on that point. Its all in the VCMX Manual
It can all work, its just that it was ordered as a MUA and configed for that.
Get someone to calculate the energy savings of conventional mode, show that to the owner, get permission to connect that return air, (for unnoc times) and Wattmaster will hook you up . (Hmmm you may need dampers in there)

I have a printshop that I set up exactly that way, but was originally MUA with building pressure control, exhaust and dehum with heatwheel and reheat.

It works nice. Presently is all OSA except during the 1 hour lunch and from 11pm-6am. During those hours it runs conventional. When they shut the press down, it opens or closes (cant remember) BI 1 i think it is and switches the mode over.

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[Dan_G]

I just wanted to say thanks for all the responses. They were all very helpful. When I first started I was not even thinking about the unit using 100% outside air. So the initial responses already had me prepared for this possibility. This was the first time I used my AAON handheld so it’s been a nice learning experience for me. I believe we are just waiting for the indoor temperature sensor to come in. Once we get the part, we will be going back and I’ll let you know how we are doing sorting out the building pressure issues and anything else that crops up.

[Dan_G]

Just a quick update. As folks may recall, the focus of this thread was an AAON unit that was configured for 100% outside air and no indoor temp sensor. It was not controlling the indoor space temperature – because it was never designed to do that.

The short story is, we found that the unit had return duct work. I had planned to basically turn the unit into a normal RTU by using the return duct work and adding and indoor temp sensor. As a short term work around, I basically disconnected the outside air dampers and set them to draw air from the return duct (0% outside air). The short term result from the last few months is …. all complaints went away and they are happy with the temperature in the space. How about that.

So I’m not sure what we will do next. I have the indoor temp sensor. We do quarterly maintenance there anyway, so we go back every 3 months no matter what. So I suppose we will see if the temperature in the space is OK once the summer really hits. If it’s all good – I guess we will leave it as-is.

[pecmsg]

Being 100% OA it shouldn’t be connected to a return.
It is trying to make up for all the exhaust fans in the building

[71CHOPS]

Just a quick update. As folks may recall, the focus of this thread was an AAON unit that was configured for 100% outside air and no indoor temp sensor. It was not controlling the indoor space temperature – because it was never designed to do that.

The short story is, we found that the unit had return duct work. I had planned to basically turn the unit into a normal RTU by using the return duct work and adding and indoor temp sensor. As a short term work around, I basically disconnected the outside air dampers and set them to draw air from the return duct (0% outside air). The short term result from the last few months is …. all complaints went away and they are happy with the temperature in the space. How about that.

So I’m not sure what we will do next. I have the indoor temp sensor. We do quarterly maintenance there anyway, so we go back every 3 months no matter what. So I suppose we will see if the temperature in the space is OK once the summer really hits. If it’s all good – I guess we will leave it as-is.

sometimes stopping complaints is what we have to do.....right or wrong.

like pecmsg said, that unit was making up all the air that is lost through the hoods. so you may have created another problem by solving one.

I would start investigating the kitchen design.....look at the hood, and exhaust fan, then look around for another makup air unit. It could be that the kitchen has a MAU that is capable of keeping the kitchen free of contaminants. you may want to experiment with opening the dampers on the cafeteria unit to provide some fresh air, as you would want the kitchen to be negative to the cafeteria, and the cafeteria to be negative to the rest of the building.

[Dan_G]

Thanks for the comments. I am aware that I have taken away the make-up air – so the building pressure is changed – it has to be more negative now. The building was unoccupied for a while, I believe it is in regular use now. So I'll hear about any problems soon enough.

The building was was divided in two separate spaces several years prior. So it probably does not need all that make up air since the kitchen is probably half the size. The AAON running on 100% outside air is really the wrong machine for the space – they need a regular RTU with a thermostat to control the temperate in the cafeteria. It's just what was on the roof from the original design of the building. Given the current layout, if they need make-up air, they should probably rely on another make-up air unit. They may actually have other provisions for make-up air. We only handle half of the equipment on the roof - there may be another MAU on that roof that we don't service. We will find out soon enough. I go back every few months. So I will investigate. Also, it's going to be hot and the complaints will be coming if the system is not working well enough.