View Full Version : Energy consumption

08-02-2013, 12:32 AM
(this querie follows a discussion I had with our Cheif Electrical Engineer this morning).

Back ground for those outside of Australia. I am based in Alice Springs, Central Australia. Presently, our temperatures are ranging from an overnight low of 26 degrees celsuis to 40 degrees celsius. The building I operate is an airport, open plan, and have packaged refrig units (x26)

Now for my query

I intend putting my building temps up by 2 degrees in order to conserve some energy consumption, but maintaining comfort conditions. This means I will raise the indoor temp from 23 to 25, with a dead band of 2 degrees.
If I put the temp up by this amount, then I check the energy consumption via the meters at the same time each week, how would I/could I calculate the amount if energy used per degree difference (so, if I used 1000kWh when the units are running at 23, then I set the AC to 25, and the energy usage is then 990kWh, what is the temp diff actaully acheiving).
I would think that the calculation would be a "curved" line.

Any input would be greatly appreciated.

08-02-2013, 01:12 AM
Hi tbowes
If you reference AIRAH degree day cooling charts for your region, this will give you an idea of the local conditions. Then ASHRAE 65 comfort chart and you can vary the increased temp conditions to maintain comfort conditions. You could do it for a few months and check the previous yeas electrical consumption for that period of months. This is all guess work of course but pretty close. Savings will be worthwhile and the equipment will last longer.
This way on a really hot day we can catch a plane to the airport and check out every one wearing swim suits Haha.
You will need to download energy consumption charts from the local supplier to show when, where and how much energy you have saved - your engineer will be supprised.

08-02-2013, 01:59 AM
Anything below +40' C would be comfortable if standing around an airport. By increasing control setpoint reduces compressor loading costs and run time. Even at Alice Springs the current supply air temp will create a high latent load as well, increasing air flow will reduce latent load , and save energy costs, will be possibly draughty-ish.

08-02-2013, 02:10 AM
Sorry. I should explain. I am a mechanical engineer (HVAC), so I am aware of temp charts, latent loads etc. Yes, increasing air flow by way of retroing some ceiling fans should also reduce internal temps by 1 degree. And this is another option I will weigh up in regards to overall costs.
What we are trying to nail down is (for example);
Increasing the set point x 1degree C equates to overall energy being reduced by xxx kWh. Thus, with each degree we equate with ?kWh.

08-02-2013, 04:56 AM
http://www.savepower.nsw.gov.au/business/power-saving-tips/increase-the-temperature-setpoint-when-cooling.aspx says up to 10% for 1 degC. Or you could contact the manufacturer for data on consumption for a range of ambient temps.
To calculate with any degree of accuracy would need a pretty good computer program with lots of data. The main parameters would be U Value of building, enthalpy difference, solar insolation etc. Got a visitor must go - good game of chess waiting

08-02-2013, 07:05 AM
The above would be assuming the units are well matched to the load. If like me at home I have a unit that runs 100% of the time once the temp is over 32 degC to get 24 degC in the room with door open (to cool surrounding rooms a little). There would be almost no savings.
My little unit at home is just enough to prevent very uncomfortable conditions, not to provide comfortable conditions.

08-02-2013, 05:10 PM
If you have data for previous years including ambient temperature and kwh used then it should be easily done? If ambient temperatures have increased then you may not see any savings but just be maintaining the status quo? Monitoring software ranges from huge money to free, depends on what hardware you have.


09-02-2013, 12:54 AM
Your local power supply company can possibly give you consumption trend graphs even on a daily basis, even better if the HVAC is metered independently. Get the previous X months records and compare to local weather conditions, available from Met office, then you can get a consumption trending relationship. Raise set pionts and compare changes in consumption. Being a commercial customer you will have peak load penalties, fixed line supply charge and a unit cost ( Kw/hr ). If a BMS is controlling HVAC concider a full night time air purge of structure, full outside air and no mechanical cooling. That alone will save power consumption.

10-02-2013, 11:53 PM
The power authority supply our estate. Being an airport (and ex federal set up) we are the authority thereafeter. I have the mech services broken into 2 sections and metered. Unfortunately, whoever was a part of setting up the BMS had no idea as to what info is relevant, and so I have no SA or RA temps. This would have given me a great insight into the energy being used.

Anyway, moving forward, I will try and get some parameters via meter readings, ambients and the set temps.

Yuri B.
25-02-2013, 05:24 PM
Should save about 4% energy for each C grade raised up

01-03-2013, 04:17 PM
what do you mean by c grade


03-06-2013, 10:02 AM
Does anyone know of any affordable three phase watt meter?