Recently I had to select some small and some medium sized fans for a sustainable project.
The small fans were a breeze: it was a light commercial building, so I went with residential quality exhaust fans. I selected them from the Energy Star excel list of qualified fans:
http://downloads.energystar.gov/bi/qplist/vent_fan_prod_list.xls
These lists are available for all Energy Star certified equipment, and are great tools for selecting them: find a good performance index (for fans, I used CFM/watt) and then select one of the better performing, reputable manufacturers.
I put the CFM/watt effectiveness requirement right on the drawing, so that I would be guaranteed the performance I wanted from what was installed. I could also provide a good list of alternate suppliers who also meet the efficiency standard right from the Energy Star list.
The larger fans were much harder. I used a fan selection program from a major manufacturer to determine which kind of fan they sold would be in the right range for efficiency and price-point, given the parameters I needed, but the program listed a variety of different efficiencies, none quite as easy-to-understand as a CFM/watt. ASHRAE lists motor efficiency requirements, and BHP requirements, but these aren't typically provided by the equipment selection program. Without some calculations and work on my part, it was difficult to even tell if the selected fans met our standard minimum efficiency requirements. I'm not allergic to work, but if energy efficiency were considered as important as other performance indicators, our industry would have standardized ratings - the EER of the fan industry.
This problem is endemic in medium-sized HVAC products. Very small, consumer goods are being provided with clear information about operation, and are benefiting from good engineering practise to reduce energy use. Very large equipment is subject to rigorous examination by engineers for energy efficiency, and is the focus of large manufacturers for efficiency increases.
Medium sized equipment -- fans in the 400cfm - 5000cfm range, for example -- seem to be left behind by today's practises, even through the majority of Noth American commercial buildings are full of them.
Monday, November 9, 2009
Thursday, March 13, 2008
Refrigeration in sub-arctic climates.
Food preservation in Canada has always been a bit of a 'hot' topic for me. We use energy to cool food in a climate that is often colder then the intended food preservation temperatures.
On a residential scale I've tried to design alternatives to the current system (packaged refrigerators that plug into the wall) but there is a certain elegance to the status quo. Here's why.
Most of the time in Canada it's cold. The refrigerator is a heat pump, and it takes heat from the inside of the refrigerator (where we don't want it) and puts it in the kitchen - in the wintertime, a place where we do want it. Although better heat pump efficiencies would be realized by placing the condenser coils outside, we would then be transferrring heat from inside the refrigerator (which, you'll remember, was first generated using the house's furnace for the purpose of heating the house) to outside the house.
Condenser cooling with outside ambient air would have much better efficiencies, of course, but the electricity isn't wasted by the compressor - it also heats the house. So maybe the status quo isn't so bad.
The system could be improved by rejecting to a water loop, instead: you could then move the heat more readily from behind the refrigerator to places it was really wanted.
Another way I see to improve upon this system is to directly circulate outside air into the refrigerator in the wintertime. This invokes concerns of air quality, pests exclusion, moisture control, and summertime air exclusion, but seems otherwise viable. Le'ts look at the issues:
1. Air Quality
Could be addressed by a HEPA filter or maybe something of lesser grade.
2. Pest Exclusion
Could be addressed by mesh, especially in combination with a HEPA filter.
3. Moisture Control
Due to the low temperatures and moisture removal by the evaporator coil, food withers in a residential frdge without protection anyway (the crisper or packaging.) It might be sufficient to warn owners to pay particular attention to tightly wrap food in the wintertime. Controls to only exchange air when required to lower box temperature will limit fan energy consumption and moisture loss.
4. Summertime Air Exclusion.
This would require a insulating damper with tight tolerances that is freeze-resistant, which might be the most expensive part of this system.
Ideally the entire system would operatate using a maximum 6" insulated duct to an outside wall, away from contaminated air (street/driveway) and should be billed as no more difficult to install then a laundry exhaust or range hood. The duct should contain two smaller exchange ducts, so that installation is very simple. An exterior wall grille designed to prevent short cycling or air would complete the package.
Perhaps, with sufficient design effort, a way could be devised to use the same duct to remove heat from the condenser from the house altogether in the summertime.
The problem is... could the cost (including installation labour, extra materials) be justified by the savings? Could operation be rendered sufficiently simple to accomodate the needs of consumers who rarely emply lint traps or change furnace filters?
On a residential scale I've tried to design alternatives to the current system (packaged refrigerators that plug into the wall) but there is a certain elegance to the status quo. Here's why.
Most of the time in Canada it's cold. The refrigerator is a heat pump, and it takes heat from the inside of the refrigerator (where we don't want it) and puts it in the kitchen - in the wintertime, a place where we do want it. Although better heat pump efficiencies would be realized by placing the condenser coils outside, we would then be transferrring heat from inside the refrigerator (which, you'll remember, was first generated using the house's furnace for the purpose of heating the house) to outside the house.
Condenser cooling with outside ambient air would have much better efficiencies, of course, but the electricity isn't wasted by the compressor - it also heats the house. So maybe the status quo isn't so bad.
The system could be improved by rejecting to a water loop, instead: you could then move the heat more readily from behind the refrigerator to places it was really wanted.
Another way I see to improve upon this system is to directly circulate outside air into the refrigerator in the wintertime. This invokes concerns of air quality, pests exclusion, moisture control, and summertime air exclusion, but seems otherwise viable. Le'ts look at the issues:
1. Air Quality
Could be addressed by a HEPA filter or maybe something of lesser grade.
2. Pest Exclusion
Could be addressed by mesh, especially in combination with a HEPA filter.
3. Moisture Control
Due to the low temperatures and moisture removal by the evaporator coil, food withers in a residential frdge without protection anyway (the crisper or packaging.) It might be sufficient to warn owners to pay particular attention to tightly wrap food in the wintertime. Controls to only exchange air when required to lower box temperature will limit fan energy consumption and moisture loss.
4. Summertime Air Exclusion.
This would require a insulating damper with tight tolerances that is freeze-resistant, which might be the most expensive part of this system.
Ideally the entire system would operatate using a maximum 6" insulated duct to an outside wall, away from contaminated air (street/driveway) and should be billed as no more difficult to install then a laundry exhaust or range hood. The duct should contain two smaller exchange ducts, so that installation is very simple. An exterior wall grille designed to prevent short cycling or air would complete the package.
Perhaps, with sufficient design effort, a way could be devised to use the same duct to remove heat from the condenser from the house altogether in the summertime.
The problem is... could the cost (including installation labour, extra materials) be justified by the savings? Could operation be rendered sufficiently simple to accomodate the needs of consumers who rarely emply lint traps or change furnace filters?
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