Fan box issues

[womb_h]

I have a mixed system olded bypass fans and new std fan boxes, the issue is the older boxes put 25-30% un-conditioned air into the occupied space. This blow 60-65 degree air on to our employees which makes them cold. The reverse happens in the summer, hot air from the plenum is blown back into the occupied space. After a 2 week engineering review the engineer is recomending we add 5 plenum heaters (this makes sence heat the plenum) but the second recomendation is to add filters to up the pressure in the fan box to reduce the amount od heated air entering the fan box from the plenum. I don't see how this will work ?? any thoughts ?

[Chris_Worthington]

I have relocated your question over to the commercial section of the site

[Chris_Worthington]

1st off welcome to the site

2nd, would like to ask a few questions;

You're relationship to this would be?

The area served is what office space I would assume?

The problem is more towards the exterior or interior?

How many boxes? served by how many pieces of primary equipment?

The type of control system is place for zoning is?

How long have you been in this place?

Do any of the boxes currently have re-heat capabilities?

Any more information you could provide us here?

[womb_h]

I am the Facilities manager for the site
this is office space ( 3 floor basement 25k sqft, first floor 50k sqft, top floor 50k sqft) there are 5 trane roof top 50 ton RTU older inlet vane units.
we are running a solidine EMS system
there are 30 controllers in the area
all exterior fan boxes have electric heaters

This is only for the top floor( only one occupied right now )

[Chris_Worthington]

recomendation is to add filters to up the pressure in the fan box to reduce the amount od heated air entering the fan box from the plenum.

I am not sure I understand your question/statement here, could you explain perhaps in greater detail?

Did the engineer mention anything about diffuser placement? anything about demand based ventilation? anything about resetting the discharge air temp from the primary equipment based off demand from the served zones? The problem is all over the floor or just in a given area?

Is there more to this engineers report????

[womb_h]

The top floor is split into two areas (east and west) both areas have thw same problem, but my production area is the worst. last summer I needed 10 move and cools to keep the area under 75 degrees.

The dampers are controlled by the EMS and open and close as needed ( this was actualy physicaly checked for functionality ).

The fresh air supply for the area is supplied directly from the plenum ( Not ducted).

With the mixed system 60% of the fan/vav box fans stay on all the time. the other 40% go on and off based on meeting temp. set point.

The over all issue is when the temp is met on the bypass fanbox and the coil shuts down unconditioned air is blowen into the conditioned sapce causing the issue.

[Chris_Worthington]

The top floor is split into two areas (east and west) both areas have thw same problem, but my production area is the worst. last summer I needed 10 move and cools to keep the area under 75 degrees.

You needed to move 10 diffusers or 10 series VAV boxes? And although your distribution of conditioned air might be screwed up, you're saying that "NO" area made setpoint and the RTU is functioning properly?

The dampers are controlled by the EMS and open and close as needed ( this was actualy physicaly checked for functionality ).

Open as in On/Off or do they proportionately open/close based off of demand? In the boxes with the fans and re-heat you're saying that the fans run during the cooling mode? or just during ventilation?

The fresh air supply for the area is supplied directly from the plenum ( Not ducted).

This makes ZERO sense are you sure?

With the mixed system 60% of the fan/vav box fans stay on all the time. the other 40% go on and off based on meeting temp. set point.

Parallel or series VAV boxes?

The over all issue is when the temp is met on the bypass fanbox and the coil shuts down unconditioned air is blowen into the conditioned sapce causing the issue.

This engineer came into the picture how? Have you had a mechanical or controls contractor view this and make any recommendations?

Have you received other opinions on this? This is just not making much sense.

Perhaps others will chime in here and attempt to decipher.

[womb_h]

There are both Parallel and series fan boxes in the area. The series boxes cause the basic problem. When the series (constant volume) boxes coil shut down the box takes plenum air and dumpes in to the conditioned space( hot during the summer and cold during the winter). The fresh air supply comes directly from a roof vent into the unconditioned plenum. This is how we are adding fresh air to the building (no ducted fresh air supply ). the dampers are proportionately open and closed ( 20% min and 80% max) based on demand.the series fan boxes run all the time, the parallel boxes turn on and off as needed.

The main problem is the series boxes pushing unconditioned air into the conditioned space. The engineers fix is to add electric plenum heaters (50 KW) to the plenum. This should fix the cold air problem during the cold months. His fix for the hot months i dont feel will work. He is asking to put new filter kits on thwe series fan boxes this will add back pressure to the box to reduce the amount of plenum air used. !!!!

I don't feel this will work .

[Chris_Worthington]

There are both Parallel and series fan boxes in the area. The series boxes cause the basic problem. When the series (constant volume) boxes coil shut down the box takes plenum air and dumpes in to the conditioned space( hot during the summer and cold during the winter). The fresh air supply comes directly from a roof vent into the unconditioned plenum. This is how we are adding fresh air to the building (no ducted fresh air supply ). the dampers are proportionately open and closed ( 20% min and 80% max) based on demand.the series fan boxes run all the time, the parallel boxes turn on and off as needed.

The main problem is the series boxes pushing unconditioned air into the conditioned space. The engineers fix is to add electric plenum heaters (50 KW) to the plenum. This should fix the cold air problem during the cold months. His fix for the hot months i dont feel will work. He is asking to put new filter kits on thwe series fan boxes this will add back pressure to the box to reduce the amount of plenum air used. !!!!

I don't feel this will work .

Me either

I do believe there is a better way and one thing that comes to mind first and foremost is gaining control over what you currently have.

Your outside/ventilation air being introduced in this manner is ridiculous and has trouble written all over it. You could be using this air to free cool when needed and it could also be introduced for ventilation air when needed via your existing supply duct system, your existing RTU's and CO sensors located in the space/return.

These older RTU's are what Trane's SFHA series? They have the capabilities to introduce and control/economize your fresh air supply to the space. Not sure why this being overlooked here?

I feel that there is more information here not givin in these brief postings, as these recommendations exclusively seem to me as ridiculous and hard to believe.

This one and only one engineer has viewed this and no others have? I find this doubtful that there is no mechanical or controls contractors involved here.

[Chris_Worthington]

Gonna make another move here, now knowing a bit more, to the controls section of the site.

Hold on here we go

[Tech23]

I agree, that a mechanical contractor should be involved and able to look at this. It could just be a controls issue and the engineer is wanting to add heaters, but that will not solve your summertime issue.

You need to have an experienced mechanical contractor look at the systems to see if everything is working properly...this may save you money and hassel in the long run.

[Tech23]

Oh and by the way...welcome to the site, glad to have you with us.

Good luck.

[womb_h]

Hi all thanks for the info.

I do have a mechanical company involved, the issue isthe start up of an older building (built in 1998) that has been shut down for 5 years. we spent 2 Mil in refurb with out any facilities people on site. The GC and arch. were handling all issues. We moved into the building in july and have had nothing but issues with heat and cooling. I requested the engineering firm re- look at what is here and my earler post was their responce. I have a 10% hold back ($200,000) and wher I am still not pleased with the way the systems run and don't paln to pay the GC the rest just yet.

They keep telling me I not an HVAC eng. and I know this but what I currently have and what they are proposing doesn't work this is why I was looking for additional inputs from some pro's.