How to get 100 degrees out of 55 supply

[stephen mendoza]

I have a VAV box with a boiler coiler in it with a duct

supply of 55 degrees. How hot would the coil need to be

to get a 100 degrees out of the runs?

[klrogers]

double post

[klrogers]

You could do it with 101º water if the coil had enough rows, static pressure would need to be higher to push the air thru' this 20-40 row coil. Truthfully, there is not enough info to answer the question, need airflow, coil size and rows etc.

[stephen mendoza]

I have a building that puts out constant heat during the

winter. The outside stat brings on the boiler and the fan

boxes for the coils. My RTU is constantly putting out

55 degrees to the building for the vav boxes to cool the

rooms down. Well, my one problem is in one space there

are 3 rooms that has one vav box with a heat coil and no

perimeter heat. What I'm wandering is my supply to the

building suppose to be higher than 55 degrees? Because

it'll bring in outside air in the winter time.

[tim fox]

You can run your rtu discharge temp at a higher temp as long as it will not hurt other zones in the building. I have a building that has a combination of vav and cav zones and if I don't run the discharge @ 60 deg in middle of winter, the cav zones won't reheat enough.I think that is what your asking.

[joken]

I would try increasing the DAT setpoint until I got complaints from interior zones then back it down. Is your boiler on a reset schedule? Turn the water temp up. I have a VAV system that was converted from a old constant volume system and with the increased volume of air I have problems getting enough heat out of some coils. You will probably have to lower the temp again next summer. Ken

[maxster]

drop the box on that 3 zone perimeter area and install a fan powered VAV...when you call for heat the VAV 55F will damper off and the fan will pull rturn air to supply the zones plus your wet coil temp. then without touching the rooftop and effecting the other interior zones on the cooling side.maintain your 55F on that rooftop and work the space heat generated within especially on the perimeter where it is missing baseboard.

[flange]

you would need much more info to get the correct answer. you dont necessarily need 100 degree air to heat that area. design supply air temp? hot water temp? cfm, heat loss, type of box? etc.

[jschaible]

Originally posted by flange
you would need much more info to get the correct answer. you dont necessarily need 100 degree air to heat that area. design supply air temp? hot water temp? cfm, heat loss, type of box? etc.

Flange is right, we need more information. If the system is designed right, you shouldn't have to change th DA-temp. Don't know if you system is pnuematic or ddc. Your vav box should have heating cfm setpoint. Typical boiler water temps are from 160-180 degrees, should vary if based on a outdoor air reset schedule. Make sure your reheat valve is opening fully. Need to fully test out vav box, check all the above mentioned by flange.

[core]

Lets assume this VAV box supplied 1000 CFM with an inlet air temp. of 55 Deg. To achieve a 100 Deg. Discharge air your coil would have to supply 48,600 Btu/hr.

Furthermore, assuming a 180 Supply water temp., the flow rate (GPM) thru the coil would be about 5 with a 20 Deg. Split.

Core