how to track energy cost on my building?

[nitrousbaby]

Im new to this site but I ve already got lots of useful info on here. I am in charge of the HVAC area of a fairly large church and I am wanting to figure out if its cheaper to cool the building with my centrifical chiller or by building ice with the screw chiller and then burning it throughout the day. I was woundering how use guys would go about tracking the cost of these two options.

 

[jraef]

From an electrical standpoint, the only thing that matters is going to be kilowatt hours. A kWh meter is as good an instrument as any from that standpoint, but that would be empirical data, not a way of predicting performance. For that you probably need to post that question in the HVAC/R forum.

http://eng-tips.com/threadminder.cfm?pid=403

What they would know better are the issues of performance and efficiency differences, climate conditions that would affect your choices etc. Be sure to post as much data as you can think of, i.e. where (in the world) your church is, size, general shape of your indoor structure, usege etc.

 

[davidbeach]

You also need to know whether or not you are paying time-of-use and/or demand charges on your power bill. If neither, your centrifugal chiller will almost certainly be less expensive as it is highly likely to be more efficient than making ice. On the other hand if you have distinctly different rates day and night you may more than offset the difference in efficiency. If you have substantial demand charges and the screw chiller is significantly smaller than the centrifugal chiller you may also overcome the difference in efficiency.

 

[nitrousbaby]

thanks alot guys Ill post it in the hvac section but yeah we build ice on off peak times that fall between 10pm and 8 am. its a 600 ton screw and 550 centrifical.

 

[waross]

The efficiency of a refrigeration unit in BTUs per KWHr decreases as the temperature difference increases.
The maximum attainable BTUs per KWHr will be much less with the ice machine than with the air conditioner.
To compare, I would track the amount of ice produced per KWHr and cconvert to BTUs per hour. Then estimate the actual BTU per hour output of the air conditioner. Measure KWHrs for both machines, convert to the same time base and compare costs.
respectfully

 

[davidbeach]

The ice machine will always require more energy, but if you are on a time of use rate from the utility, making ice at night can be less expensive even though it uses more energy. If you don't have time of use rates don't even consider the ice machine since it is larger than the other.