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Radiantly heated floor with vav terminal units

Radiantly heated floor with vav terminal units

Radiantly heated floor with vav terminal units

    I have not used this forum before and hope this is an appropriate subject.
    I am searching for suggestions for control strategies.
Setting:  Child's reading room in a to-be-built public library.  The room will have hydronic radiant floor heat and a dedicated vav terminal unit for heating, cooling and outside air ventilation.  The floor is concrete structure. The total concrete slab thickness under the room is 6 1/4".  There will be 2 1/4" of concrete, 2" of rigid board insulation, the PEX tubing and 2" of concrete on top.  The radiant system has a dedicated pump.  The building will have a DDC control system.
Problem:  How to integrate control of the radiant floor and vav systems without providing heating and cooling simultaneously and/or having the systems fight each other.  I am considering maintaining the slab at a varying temperature dependent on outside ambient dry bulb and allowing the pump to come on only below a predetermined outside temperature.  The vav would provide primary heating and cooling.
I hope I've provided enough information for responses.  If anyone has successfully put a similar system together I would like to hear about it.
Thanks, Tim

RE: Radiantly heated floor with vav terminal units

I have not designed any system quite like that one, but I have a few thoughts you may want to consider.  First of all, the floor heating, I'm assuming, is for comfort of the kids (or adults) sitting on the floor.  If that is the case, you may want to set a certain temperature to maintain the floor, independent of air temperature.  If this is a ground floor, the ground temperature may cool the concrete below what is comfortable certain times of the year (depending on location).  Alternatively, there is a method (I believe the ASHRAE Fundamentals book describes it) to determine the appropriate place to turn on baseboard heating if you have a heat pump.  Modeling the floor heating as the heat pump, you may be able to use the same method to determine what limiting factor you want to use for the VAV system in fall and spring (and even winter, depending on location).  Hope this helps some.

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