Chilled Beams vs. Variable Refrigerant Flow

[AECenter]

Can somebody give me a scenario when chilled beams would be the preferred method of conditioning and ventilation as opposed to the variable refrigerant flow systems?

I have heard a lot about chilled beams, but I'm not sure they are ever going to really get popular in the US, because I don't see how they can compare with the DX systems.

Just looking for some good info for an article I want to put together.

Thanks for the help.


-chris
aec.us.com

 

[russ_watters]

It seems an oddly framed question since I don't see how chilled beams and variable flow Dx systems are necessarily directly in competition with each other:

Chilled beams need a constant 20-30% primary air for induction and they need it dehumidified so there is no condensation at the chilled beam. They use high temperature chilled water for cooling, which can make for a very efficient chiller, but even if they use normal chilled water temperatures a chilled water system is much more efficient than DX. Chilled beam systems compete with VAV and fan coil unit systems, saving a lot on fan energy.

Variable flow Dx competes with various split systems and perhaps also water source heat pumps. It can provide a nice efficiency boost if you have simultaneous heating and cooling on opposite sides of a building (so can water source heat pumps), but absent that, it won't be much if any more efficient than a typical DX heat pump or air conditioner. Certainly not as efficient as a water source heat pump.

 

[AECenter]

Thanks Russ. So if the building is large, consistently occupied, with reasonably controlled humidity then chilled beams would work well?

If the building is small and has continuously changing occupancy and demands, then out of comfort the VRF system would be the way to go? But you end up paying for the comfort in higher energy costs?

I guess where I am getting mixed signals is with office buildings, hospitals, and some school buildings. I have seen only VRF going in, but never chilled beams. I don't know why and I want to understand why chilled beams don't seem to be gaining as fast as VRF in the US?

Do you guys see lots of chilled beam jobs?


chris
aec.us.com

 

[Yuri B.]

Humidity control itself with those beams may ask more energy than fan consume in a fancoils system.

 

[AECenter]

Yuri, I wonder what the numbers are on that. This is my understanding of the basic energy principles for the chilled beams. With a VAV box system you might have a 20,000 cfm unit on the roof that provides a minimum of 2,000 cfm of Outside air. The Chilled beam system would require a 2,000 cfm unit on the roof that can produce very dry air. Running the fans in a 20,000 cfm unit probably costs significantly more than running a 2,000 cfm dehumidifier.



Does anyone have any approximations on how much energy it would take to power a 50-ton Variable Refrigerant Flow DX system, and how much it might take to run a 50-ton Chilled Beam system? Any info would help.


Thanks,
chris
aec.us.com

 

[russ_watters]

Humidity control itself with those beams may ask more energy than fan consume in a fancoils system.

Conservation of energy demands that the output must be equal and since chilled water systems are more efficient than DX, you almost always save on the input.

 

[russ_watters]

Thanks Russ. So if the building is large, consistently occupied, with reasonably controlled humidity then chilled beams would work well?

Yes. With a chilled-beam system, as with a fan coil unit system, you still need a centralized outside air unit.

If the building is small and has continuously changing occupancy and demands, then out of comfort the VRF system would be the way to go? But you end up paying for the comfort in higher energy costs?

Chilled beams do not reduce comfort vs VRF systems.

I guess where I am getting mixed signals is with office buildings, hospitals, and some school buildings. I have seen only VRF going in, but never chilled beams. I don't know why and I want to understand why chilled beams don't seem to be gaining as fast as VRF in the US?

Do you guys see lots of chilled beam jobs?

The main reason you see VRF systems in those buildings is that light commercial and small institutional building owners are cheap, so first-cost tends to trump all other considerations when building a new building. Though it surprises me about hospitals - most I've worked in have chilled water systems.

My company deals almost exclusively with lab buildings, which almost always have a chilled water system available.

But the major reason I think not a lot of chilled beam systems have been installed in the US yet is that people are set in their ways and take a while to change how they do things.

 

[AECenter]

Russ, do you know of any sites that have an energy consumption comparison between Chilled Water systems and DX systems?

I'm sure I could do a study of my own, but maybe you know of a good one that has already been done?

Thanks,
chris
aec.us.com

 

[russ_watters]

Googling finds chilled water system efficiency easily enough: http://automatedbuildings.com/news/jan01/articles/hartman/hrtmn2.htm

That link lists "good" as 0.7 to 0.85 (annual average) which sounds about right to me. The air handling units will be another .2 or so (chilled beam a little less).

DX systems are governed by code requirements and since they are packaged and simple, their efficiencies are published by the manufacturers. Residential systems are required to be 13 SEER (13 BTU/Watt = .92 kW/Ton), but commercial systems are still allowed to be 10 SEER (1.2 kW/Ton).

 

[AECenter]

Funny thing. There is a project going on down here in San Antonio called Texas BioMed Phase V. They have a 160 ton VRF system laid out, while at the same time they are very concerned with energy efficiency. It's a big life sciences building.

Thanks for the info, Russ. I really appreciate it.


-chris
aec.us.com

 

[russ_watters]

You're welcome, but just to be clear, what I was discussing above is for standard DX only. VFR (or water source heat pump, for that matter) can have significant potential for improved efficiency in situations where there is simultaneous heating and cooling.

For labs, you can also have simultaneous heating and cooling in the same zone or all zones at the same time. So it often makes sense to use a heat recovery chiller, which makes hot and cold water at the same time.

 

[AECenter]

Really, a simultanious heating and cooling chiller... I'm going to have to learn about that.

By the way, when you are doing labs do you get into fume hoods? I used to rep Phoenix Controls up in Boston, and half the engineers I knew didn't like how the fast acting valves actually don't measure the air passing through it. The valve just responds to an open/close signal and moves to a pre-programmed position. They preferred valves that moved slower, but actually measured how much air was passing through the valve. Have you ever run into this?


-chris
aec.us.com