[Bldg-sim] Radiant slab Heating Cooling

Peter Simmonds peter.simmonds at ibece.net
Thu Feb 23 08:38:22 PST 2012

Varun, your perception is nearly true, but it depends on what you are modeling? If you are modeling the energy performance of a building a four pipe fan coil works just fine as it maintains the required energy balance. It is true that the actual performance of a radiant floor is different than a fan coil, but you are looking at energy and not optimal modeling.
Your thoughts on stratification are somewhat correct. I would tend to think that stratification is caused by space heat load and air movement, especially displacement. Yes, there is a convective flow from the floor but this is quite small as the temperature difference between the floor surface temperature and the space operating temperature.
Regarding temperature; this depends on what program you are using and why you want to segregate the different temperatures?

Peter Simmonds, Ph.D.
Senior Associate
Head of the Advanced Technology Group
IBE Consulting Engineers
14130 Riverside Drive, Suite 201
Sherman Oaks, CA 91423
d: (818) 305-3246 o: (818) 377-8220 f: (818) 377-8230

Ideas for the built environment
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From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of varun kulkarni
Sent: Thursday, February 23, 2012 5:34 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Radiant slab Heating Cooling

Good Morning everyone,

I have been reading through the archives for modeling radiant slab heating and cooling.
Most popular and the closest to real world approach I found was using a 4 pipe fan coil unit and making the fan energy zero.
I still have following questions:

*         Did anyone think of using a factor, which when multiplied to the energy usage by fan coil system, give us the actual energy usage by radiant system. (I would guess it would be <1)

*         As radiant heating and cooling forms a stratification layer in the space. And  we care about first 6-8 feet to be within desired temperature range. So to take that into account while modeling "it"  as fan coil unit, can we lower the ceiling height. Does that mean the conduction load from ceiling/roof or the wall above 6-8 feet doesn't count ?

*         The temperature range for heating water (95F-105F) and cooling water (55F-65F) pumped in the radiant system is different from the typical chilled water (44F-45F) and heating water (170F-180F). How do we make sure our model reflects this while using fan coil unit.

I am sure there are more questions you would have come across but these were some of my major concerns and I would appreciate any inputs/ suggestions.
PS: This is a aspiring LEED platinum building.

Thanks and Best Regards,


Varun Kulkarni

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