Hot water re-heat coil & baseboard convector sequence of operation

[Cjrac]

Hi Guys, I have an application where the main air handling unit (constant volume) is providing slightly cool air (65 deg F) to both interior and exterior zones. Each zone has its own re-heat coil. The exterior zones also have a baseboard convector heater. I am unsure of the best way to sequence the re-heat coil and baseboard. The re-heat coils will be sized for a delta T of 20deg F. No air conditioning is required for this building. Any suggestions? Thanks.

 

[SAK9]

Is the air handler only used for supplying ventilation air?If that is the case it is best to supply air at room design temperature.Anyway the air quantity supplied in such a configuration will not be significant enough to effect a room temperature change.As for the baseboard,I would use weather compensating control on flow temperature of hot water and thermostatic valves on the baseboard heaters

 

[willard3]

You haven't told us enough about the CV air handler and its use. If it's only being used for OA, what Sak9 says will work fine; if it's being used to heat, control will be different.

 

[Drazen]

what is your cooling interior design temperature?

i am not sure what do you plan. reheat coils are used for cooling season, while baseboard heaters are used for heating season.

you neither use reheat coils for space heating nor you use baseboard heaters for reheating, that's for sure. so there is no control sequence between them at all.

 

[ChasBean1]

Cjrac, when you need to heat, modulate the box (if there is one) to minimum VAV and then first open the convector heating. Why? Because heating or cooling via water flow is better than heating or cooling by airflow, because air has less specific heat capacity than water. If the perimeter water heating system has done its full duty and cannot do more, then open the reheat coil valve.

 

[willard3]

Reheat coils are used frequently for heating.

 

[cdxx139]

Your first stage of heating should be the box min w reheat, set discharge to 72. If setpoint canot be maintained, and second stage should be baseboard. Whatever sequence you use, make sure the baseboard is not fighting the box.

knowledge is power

 

[Drazen]

it seems i have misread original post, turning my attention to "slightly cool" air and considering reheat only as addition to dehumidifier.

what confused me, over my low attention, is the concept of "slightly cool" air. there must be some reasonable explanation of it. normally, if temperature-neutral air would be sent to spaces on heating season, that should be "slightly warm" air, few degrees to cope with thermostat range and small inaccuracies, a common practice, a specifying exact design temperature for supply air could easily lead to slight subheating.

slightly cool air could mean that interior spaces likely need no heating in winter but some level of heat rejection.

anyhow, i would stay with chas, baseboards heater should have precedence in perimeter zones most of time, though "slightly cool" supply air concept did not point in that direction.

 

[NegativeZero]

you have a constant volume system that supplies a constant air temp you set. 65 winter 55 summer. you have interior reheats that kick on when that zone drops below the room set point or when someone jacks the stat up to 80. are the reheats electric or HW and do these zones have modulating dampers?

the perimeter hot water can be controlled by using a Water Temperature Setback control, controlled by outside air temps for example- 0* OA = 180* water to 50* OA = 110* water. boilers shut down at 55* OA or interior space temp. all depends on the control you have.

I bet this building has 4 zone for the perimeter and no real individual zone control for office's, they may have dampers on the baseboard or a danfoss valve at the beginning, if your lucky.

there are a few was to do this. need more info