Water Pipe Freeze - Open Parking 2

[Designer_82]

Project I'm working on has an open parking garage that will have a Drop Ceiling.
Design requires some hot & cold water pipes routed above this drop ceiling.

HVAC engineer provided unit heaters above in order to prevent the pipes freezing.

My question is whether the unit heaters provided would be adequate to keep the pipes from freezing considering it's an open parking garage.

Drawing can be viewed here here:

https://ibb.co/f8hjVK2

 

[LittleInch]

Why not lag and trace heat them instead using an auto tape activated at say 5 C.

Heating a void looks very wasteful

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[3DDave]

A heated area above a drop ceiling in an open parking garage is likely to have a large number of small residents moving in over the winter. Heat trace and insulation over that to slow the outward heat flow seems a much less attractive situation for the local wildlife.

 

[nuuvox000]

We do this all the time; there is typically insulation on top of the panels of the dropped ceiling. From there, it's simply a question of load calcs. Not exactly sure why they like to do this over heat trace. Maybe just with all of the p-traps and other piping, the electrical install cost is too much. Some of these people sell these buildings so they don't care much about operating costs.

Never thought about the animals moving in; that's a great point.

 

[Snickster]

You can do a heat transfer calculation of the space inside the drop ceiling for coldest winter conditions to determine the heat loss from the ceiling space and the surroundings.

Heat loss is equal to Q = UAdT (heat flow Q is in Btu/hr)

where U is the overall heat transfer coefficient of the walls and ceiling Btu/(hr-ft²-deg F)
A is the surface area of the walls and ceiling in ft²
dT is the temperature differential between the ceiling space and the surroundings = Desired space temperature minus ambient temperature at coldest winter design day in deg. F

I assume the top and side walls are concrete so these can be grouped under one set of equations with common U value determined as follows:

R total = R inside surface air film + R concrete (assume 12" thk) + R outside air film = .61 + 1.2 + .17 = 1.98
U = 1/R = 1/1.98 = 0.5 approx.
Q = 0.5(A)(Tspace - T ambient) This is the heat transfer through concrete ceiling above and around space

For drop ceiling:

R total = R inside air film + R layer of insulation + R ceiling (acoustic tile or gypsum?) + outside air space
= .92 + 8.0 (assume 2" thick at R=4 per inch) + .45 (assume 3/4" gypsum board) + .17 = 9.54
U= 1/R = 1/9.54 = .104
Q = .104 (A) (Tspace - T ambient) This is the heat transfered through the ceiling

Heat transfered through ceiling + concrete at design temperature must equal heat input by the unit heaters.

 

[Alistair_Heaton]

the way they deal with this in scandiland/germany is lag with hemp infused insulation which criters won't nibble. Same with wiring insulation hemp. They use it in cars as well these days.

 

[BronYrAur]

can you glycol the piping?

 

[LittleInch]

Don't think I would like glycol in my tea....

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Also: If you get a response it's polite to respond to it.

 

[BronYrAur]

Hmmm I see "hot & cold" water pipes in the description, but I only see heating hot water pipes on the drawing. Are there really domestic plumbing lines in the ceiling or just heating hot water?

 

[LittleInch]

Had to download the drawing to expand it but yes looks like HW heating pipes to me.

Send like a good idea to lag / insulate them to me.

Glycol though reduces heat capacity.

OP hasn't been seen since posting the question

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.