HIGH-PERFORMANCE HVAC
Myths
MEASURING UP THE HE E
Setback caveats
A
fter a recent ent series of training sessions ou out west for HVAC contractors hosted by a forward-thinking over my mind some of the hinking mechanical wholesaler, holesaler I was as going o er in m industry and product issues discussed and thought it might be helpful to share some insights with a wider audience. Our industry is constantly measuring and improving the performance of products, systems and technologies, so it can be helpful to recalibrate our thinking every now and then.
Savings from setbacks are not exactly straightforward and guaranteed. For a start, the more efficient, tighter and better insulated a house is, the longer it takes for the house to cool down, meaning less time at the bottom of the setback and fewer savings to be realized.
Savings at cruising altitude As I felt the pilot take us up over 36,000 feet, I realized that he was doing ng something like what we do with setbackk thermostat ergy technology. The extra energy consumed by the plane’ss powered climb might seem like a waste of energy, but it is indeed da calculated fuel saving measure.
As well, in heat pump-based systems, if the warm-up cycle engages the “emergency” expensive electric heat, most of the savings will be lost. There are humidity and comfort concerns as well. This is why the common literature from government agencies and utilities will advise a modest 3 to 5°C setback for periods where the thermostat can be setback for more than six hours.
The energy used roughlyy equals the energy saved during the controlled gliding descent, scent, but in between there are significant energy gy savings related to the much lower air resistance ance at altitude. This winter, if you get asked if setting back the thermostat saves money feel free to use the airplane analogy. Explain the energy saved as the house cools down is roughly equal to
Gord Cooke
70
M e c h a n i c a l
the increased energy needed to heat it ba back reduc up. The fuel savings come from the reduced heat flow during the time the building is at a the bottom of the setback temperature. If it’s it’ 20°C 20° inside insid and -20 outside, ou the temperature difference is 40°C. 40°C If you lower the inside insid temperature by 5°C, the new temperature difference is just 35°C, or 11 per cent lower. So, while whi the building is at 15°C, your client will be saving more than 10 per cent of their fuel consumption.
Gord Cooke is a professional engineer who has spent 20 years helping builders and HVAC contractors iÜlement innovative technologies into high-performance homes. He has particular expertise in IAQ and airflow management in houses, and can be contacted at gcooke@airsolutions.ca.
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