Cost Efficiency of Commercial HVAC

[samara]

Does anyone have any surveys on the benefits of leaving HVAC systems running 24/7. Is it more efficient to do so rather than turning them on and off during business / non-business hours ina professional building?

Thanks in advance.

[flange]

this a kinda like the chicken/ egg question, but there have been many studies conducted over the years. a lot depends on where you live, type of construction, age of equipment, etc. a good place to start would be a qualified energy auditor. keep in mind also that every time you start a motor or whatever it puts more stress on it and related devices as opposed to running in cruise control.

[jack marcotte]

You may want to be concerned about untility rate structure,
sometimes you can save money by expending more energy at a cheaper rate. After hours rate structures are usually fractional cents/Kwh. Look into it. Some times saving energy does not mean saving money.

[alex_in_fl]

Depends upon lots of factors (Jack nailed one of them). Here are points to ponder:
1. Where is facility located?
2. How humid is the area?
3. What are night time temps?
4. How much is your HVAC system oversized?
5. Do you get night differential (Jack is on target).

If you live in humid environment then you'll likely get water (condensation) in the fixtures turning HVAC off all night. Might be okay in low humidity areas.

If night time temps are cool enough then turning HVAC off might save dollars. If not then the facility gains heat and must be cooled anyway. Note, however, the HVAC is extremely efficient if cool outside so savings probably will be minimal.

One option is to buy a programmable setback thermostat. Let building warm up 3-5 degrees at night and on weekends. You might achieve a savings doing this, especially on weekends.

Alex

[controltechnician]

A couple of PHD's did a study a few years ago to quantify the effects of setback and how it impacted energy consumption for various types of commercial buildings in different parts of the country. This study was commissioned by Honeywell. They developed a software program called the Rooftop Unit Energy 'Savings Estimator.' The Savings Estimator allows users a means to compare various setback, economizer and demand control ventilation control strategies and their estimated energy use impact. You can download it for free from http://customer.honeywell.com/buildings/CBWPDownloads.asp