Is it me, or is it a little warm in here?

April 8, 2007 7:38 PM

What form of energy is used to heat a Wal-Mart, Home Depot or Costo store, and how much does it cost per month in the winter?

Each time I walked into Wal-Mart this winter, it felt 75 degrees inside. Many times, it was 25 degrees or colder outside. A Wal-Mart Supercenter is easily 100,000 sqare feet (with high ceilings to boot). How much does it cost them to keep such a massive space heated 30-50 degrees above outside temperatures 24hrs/day for a month? And what are they heating the place with?

posted by colgate to science & nature (12 comments total)

heating with, highly probably forced air, vents along the ceiling or behind the walls. Don't know how you'll find the heating costs. Theoretically you could find how much area needs to be heated and extrapolate from there, but you have a lot of open doors/ loading areas etc variables to deal with. So, exactly... a bugger lot, I'd guess into the thousands.
posted by edgeways at 7:58 PM on April 8, 2007

Idk about large stores, but at my church (which is easily 75 feet tall), the heating/cooling system is designed to produce a "curtain of temperature" about 15 feet tall. It's just an ordinary forced air furnace-type system with floor vents, and there are also low-profile steam radiators around the perimeter. In fact, if you turn on the fans in the summer, it'll do more harm than good because the hot air is up there, and you'll disturb the "curtain".
posted by fvox13 at 8:10 PM on April 8, 2007

I'm gonna take a guess that that they are heating the place with wood pellets. I had a friend who recently moved into a firehouse (high ceilings!) and that's what he uses.

Wikipedia has some more info on the fuel itself. From what I've heard it's pretty cheap and readily available. That in combination with a forced-air system would probably do a great job at keeping a Wal-Mart cozy.
posted by thebigdeadwaltz at 8:29 PM on April 8, 2007

You'd be surprised how much heat all the light fixtures inside a place like that produce. Some office buildings have to use air conditioning to cool the insides during the winter because so much heat is being produced by lights, people, and computer equipment.

I doubt that a big shopping center like Walmart is like that, but I would bet that the lighting is the single biggest source of heat in the place, bigger even than any deliberate heating system. (That would vary depending on the outside temperature, of course.)
posted by Steven C. Den Beste at 9:01 PM on April 8, 2007

Costco and Wal*Mart are two of the most advanced companies in the retail sector with dedicated energy planners on their facility staff. You can get some background in this energystar pdf. They generally use high-efficiency heat pumps.

The innovation Costco is best known for is adding tons of high efficiency skylights to reduce their heating and lighting costs during the day. I see articles in some of the retail mags on this topic, but I rarely read them.

The link I provided claims that Wal*Mart saved over $17 million in energy efficiency programs. Nearly half of the energy cost at a store is HVAC, so that might give you some idea of the magnitude of the costs involved.
posted by Lame_username at 9:03 PM on April 8, 2007

Also note that if the primary source of heat loss is through the walls, floor, and roof (rather than through air exchange), then the larger the facility, the less it costs (per cubic metre) to keep it warm (heat loss ~= surface area).
posted by hAndrew at 9:06 PM on April 8, 2007

Although not a Wal-Mart, I used to work in a Jo-Ann ETC store (about the same size as a non-Super Walmart) and their monthly electric bill was around $1,000 or so a month.
posted by itchie at 9:28 PM on April 8, 2007

The local BJs (warehouse store, similar to Costco or Sam's Club), is heated with natural gas, I'm almost 90% sure.

In fact they just put in a new heater during the last few weeks. What I thought was interesting, is that there's no duct work. The heater is just a giant freestanding machine in one corner of the warehouse. It's probably about 15' wide, 10' deep, and close to 30' tall. It seems to suck in air through filters at the base, and blow it out through louvers near the top. I didn't look at how it's plumbed in, but next time I'll look for a gas line or flue. I'd say it might be possible that it's just an A/C evaporator/blower, but they were running it on a particularly cold day and it seemed warm near it.

In other warehouse stores (Home Depot, specifically) I've seen infrared radiant gas heaters over the checkout lines, but not at BJs: they seem to just have that big furnace/blower, and air curtains on the doors.

(This is outside DC, by the way. Not the coldest place in the world but not that balmy either.)
posted by Kadin2048 at 10:03 PM on April 8, 2007

Though not precisely an answer to the question, I thought you might be interested to know that the way they heat the Mall of America is that they don't; the heat generated by all the warm bodies, moving parts, and natural and artificial lights is more than enough for a space as efficiently large (as already noted, the larger the enclosed space smaller the ratio of surface area to volume and thus the more efficient, and it should also be noted that this ratio increases exponentially) as the Mall of America needs no external heat source. This is part of the reason why such a building is only feasible in place like Minnesota or Syracuse, NY (home to the constantly on-and-off-again DestiNY USA). In fact, the real issue isn't heating, but cooling, which even in the Midwest winters is still a problem in the MoA.
posted by ChasFile at 11:05 PM on April 8, 2007

Yeah, I didn't read the [More Inside] but wish I had, because:

In fact, and somewhat counter-intuitively, larger spaces are more efficient to keep at temperature than smaller ones. That is to say, per square foot, it often takes dramatically less energy to heat a larger building than a smaller one. So then it becomes a pretty simple min/max problem of finding the local maxima after which adding building area has diminishing profitability returns. That is, when the profit per square foot in sales is outweighed by the cost per square foot in heating (and, if you care to take into account, employee salaries, maintenance, etc.) This equation is interestingly complicated by the fact that it appears, per the Mall of America, adding square footage is FREE (at least in terms of heating) and therefore at worst cost-neutral. Hm.

This is, of course, only true up to a certain point of reasonability. A family of 4 occupying such a space is, of course, absurd and less efficient than if they occupied a trailer. However I can with reasonable certainty assure you that a big-box store almost certainly has a smaller environmental footprint than whatever number of smaller individual smaller stores it would take to stock an equivalent number of items and service an equivalent number of customers.
posted by ChasFile at 11:23 PM on April 8, 2007

(Adding square footage is FREE - after a certain point.)
posted by ChasFile at 11:25 PM on April 8, 2007

A standard commercial building needs a ton of cool air for every 300 to 400 square feet of floorspace.

A store with 100,000 square feet would need a cooling unit of approx. 285 tons. AAON, Wal*Mart's chief supplier of HVAC equipment, makes single rooftop units up to 230 tons. A "ton of refrigeration" is defined as the cooling power of one short ton (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. This is equal to 12,000 BTU per hour, or 3517 watts. Here is the average cost per kilowatt hour (10 cents). If a store of 100K sq ft runs the AC 24 hours per day, it's likely to cost $35K per month in electricity (I think).
posted by mattbucher at 11:10 AM on April 9, 2007