Dr-Fix-It! Notebook Archive:
It's Cold Inside . . .
Whenever I plan to do some grocery shopping at the local supermarket, I always take a sweater or a jacket. It is always so dad-blamed COLD in there! Even in the blazing summer heat, I need a to take a jacket or sweater to do my grocery shopping.
Once, in the checkout line, I overheard another shopper remark to the cashier, "Boy, they must be wasting a lot of money on air-conditioning to keep this store so chilly . . ."
I smiled and chimed in," Believe it or not, they are saving money by keeping this store so chilly!"
The shopper and the cashier both looked it me. By their blank slack-jawed expressions, I couldn't tell if they considered my remark utterly stupid or if it was just that the remark came from a man dressed for winter when it was 92 outside. Anyway, they went back to the business of checking out as if I didn't exist. - - -
The refrigeration equipment that runs the low temperature display cases in the local grocery store requires up to three times more electricity to do its job compared to the store's air-conditioning. The three major reasons for that relative inefficiency is that refrigeration equipment operates a much lower temperature, makes ice and must defrost the ice.
First, the efficiency of the equipment depends on the temperature it is required to produce. In air-conditioning and refrigeration, the colder the temperature needed, the more electrical energy will be used. For instance, a frozen food display case typically performs at rate of about 4 BTU's per Watt-hour of electric energy. Compare that to an air conditioner which can work at a rate of 10 to 14 BTU's per Watt-hour of electric energy.
Secondly, Air-conditioners move water out of the air by condensing it on the evaporator coil and getting rid of it in a liquid state. Air-conditioners have a pipe that connects to a pan at the bottom of the coil which allows the water to move out of the air-conditioner and right down the drain. Refrigerators and freezers remove water from the air by forming ice. That second change in state from liquid water to solid water (ice) requires an additional 144 BTU's per pound of water. Those extra BTU's cost extra bucks on the electric bill.
But, we are not done spending extra money! Now all that ice is plugging up the refrigerator / freezer's coil and reducing the efficiency even more! So we need to spend EVEN MORE energy dollars to melt that ice back into a liquid to get it to drain out of the refrigerator or freezer.
Store air enters these refrigerators and freezers every time a shopper opens the door to grab a product and when the shelves are restocked. Many refrigerators in your grocery store don't even have doors! Open refrigerated displays in the diary aisle and the deli encourage impulse purchasing by putting those cheese sticks and pickles within easy reach. Open freezers pitch the latest ice cream confection. The colder and dryer the store air that infiltrates these units, the less work the refrigerator or freezer will have to do - and that saves the grocery store energy dollars.
So, your local grocer will air-condition his store as cold as he can. The lowest temperature limit is often set by a statistical relationship between energy costs and customer comfort. Cold customers leave the store quicker and spend less. So, for each store, there is one optimum air-conditioning temperature which maximizes the customer's shopping time and achieves the best energy savings.
Maintaining the coldest, dryest air in the store as possible saves your grocery store money on the electric bill but that cold dry air tends to dehydrate the fresh produce. So, your local grocer probably has installed a misting system or some other method to keep the fresh produce wet which makes it look fresher longer.
- - - From his office above the courtesy counter behind the two-way mirror, the grocery store manager smiles and nods as he watches me do my shopping dressed in winter gear. Although it is 92 outside, it is quite chilly inside. To the the grocery store manager, I am a statistical maximum: able to withstand the cool temperature while taking a long time to shop. From the standpoint of grocery store profit, I am the perfect customer! I am actually helping to keep the food prices down!
So, STOP STARING at me in my winter jacket . . .