HVAC energy use reduction 2

[Mellvis]

I am looking at the HVAC system for a manufacturing facility that is now an office building with 2 large bays for light assembly work. The climate controlled area of the building is around 150,000 square feet. The system consists of a chiller (turbine for summer and rotary screw for winter) and it's associated cooling tower and a boiler. These items run all year long! This is new to me (most places that I am familiar with use packaged units). Every air handler and make up unit has a pre-heat coil, a chilled water coil and a heating coil. This is in Charleston SC where it does not get below freezing too often. I am working with the HVAC vendor to try to cut our astronomical utility bill by securing the chiller during the off hours and when the outside temp gets down to 55F. Obviously I would try to do the opposite with the boiler during the summer months. My thinking here being when this building (built in 1998) was used for glass manufacturing the temperature/humidity requirements were far more stringent than they should be for an office building. The system seems to be overkill and runs continuously even though this is mainly a dayshift weekday facility. Would starting and stopping the chiller and cooling tower more frequently have any adverse affects? Any other ideas on how to reduce the energy costs of this type of system are certainly welcome.

 

[imok2]

A good start might be to get fimilier with energy management stragity so try this:

http://www.pnl.gov/dsom/publications/15074.pdf

 

[MintJulep]

What a great assignment. All you really need to do is turn some stuff off a night and you're a hero. Of course it seems like you could go much further.

Start with a good load calculation of the building. Then get capacity and performance data for all the equipment. A good energy simulation program would be good to have as well. Develop a load vs. outdoor condition curve.

Rip out the pre-heat coils and associated piping. Sell for scrap. Re-pulley the fans to supply the necessary (which may be different than the current supply) amount of air with the now reduced static pressure. That is a big chunk of change saved right there.

Implement an economizer mode. Sequence the chillers so that you run the one the best matches the load, keeping your electric rate structure in mind.

 

[lilliput1]

PWI Engineering
4021 Stirrup Creek Drive, Suite 400
Durham, NC 27703
Phone 919-460-1448

Should be able to help you. You would save a lot converting the system to variable volume with variable speed supply and return fans,reheat at minimum turndown, enthalphy economizer mode, unnoccupied mode control and demand control ventilation. Fan powered terminal reheat would be required at perimeter spaces to provide heating with the AHU off.

 

[ozmosis]

On the same theme as lilliput1, fitting VFD's on the cooling tower fans will improve performance and energy saving. An added function is to get a VFD that has built in Hibernation/sleep mode. This means, that if the VFD is in it's own PI loop measuring the temperature and if the outside air drops to a level where the cooling tower is simply idling away, the hibernation/sleep mode will kick in and automatically shut down the VFD (but still in effect be 'alive')until the temperature measured started rising and then it will start again. it's an effective and simple way of saving energy.