Radiant heating and cooling

[tbedford]

I am soon to be commissioning a mechanical system using 3 water source heat pumps to heat and cool a medium-sized passenger ferry building. Does anyone have a good source to read up on applcable BAS control schemes for hot vs.cold days?

thx,tab

 

[GMcD]

If you are the Commissioning Agent, the design documents/specifications should have a written sequence of operation to follow. Didn't the designer/engineer provide one?

Is it a radiant slab FLOOR system?

Is it suspended radiant ceiling panels?

Is it a radiant slab CEILING system?

What is the ventilation system and it's controls sequence?

There is no such thing as a "canned" "standard" sequence of operations for "a radiant heating and cooling system with heat pumps", since every building and application is Model #1, Serial #1.

Hopefully if the design team has done the building design properly, the exterior climate thermal loads will be minimized, and the building systems won't need to react quickly to hot vs cold days. It also depends on how the heat pumps are piped up - can each heat pump be individually switched over from heating mode to cooling mode? Or are thay all on one primary circuit like a 2-pipe chnage-over system? A thorough understanding of the building envelope and anticipated thermal loads at different outdoor conditions will be needed before you can understand how the heating to cooling change-over should be controlled.

 

[Zapster]

A curious name for your thread because it can have two meanings. Is someone trying to use radiant cooling???? or is it a radiant heating system with traditional forced air cooling? If it is the first, then condensation will be problematic.

 

[tbedford]

thanks for the comments and i should have posted more info...

the 10,00 sq.ft. building uses heat pumps to heat a slab floor only(first stages of heat) and if required cool the slab floor as a second stage of cooling...
first stage of cooling comes from the adjacent ocean water thru a heat exchanger...
there is a boiler back-up...
there are two chilled water air handlers each about 10000 cfm...
we have recently experienced warmer than usual summer temperatures and the building operator has driven the floor temperatures too low...with you know the expected results...

slippery floor...safety hazard...not to mention water in the glue under the linoleum...

the design team did provide the control sequence but the building operator and controls tech were trying to "stretch" the system...

i never did see the OPR and I suspect the original owner's reps were different than the current team.

another day in paradise...

tom

 

[GMcD]

Ahh, then this is a clear problem - the dehumidification function and capacity of the air units must be addressed. Also building air leakage. The fundamental design and control issue of a radiant cooling system of any kind is to CONTROL THE DEWPOINT. The lower the ambient dewpoint, the lower you can drive the radiant cooling temps to get more cooling capacity. The Air units in this case must also have a dehumidification sequence to insure a controlled dewpoint.

From what you've described, the operators should NOT have tried to use the radiant floor cooling to "get" more capacity unless they first addressed the dehumidification function of the air unit(s). Also, given that there is at least 2 cfm/SF worth of air circulation, was there not enough cooling capacity in the air side? Should have been, if it was designed properly.

Normally with radiant slab systems of any flavour, they are supposed to be used for "steady state" operation- set the slab to temperature X and control that from a slab temperature sensor feedback, and use a constant flow, variable temperature circulation system. When one gets high transient thermal loads in the space, ALWAYS use the air system as the "first responder". Use the radiant cooling only if you can dehumidify low enough to allow lower radiant cooling surface temps to try to get additional cooling capacity.

 

[willard3]

If radiant cooling is used anywhere near the dewpoint of the air, you should have a dedicated outdoor air system that brings the OA way below dew point before being introduced to the conditioned space.