Recount

bryan — Wed, 31 Jan 2007 18:29:02 +0000

As if anyone really cares, I actually checked out my numbers on the heat pump. It turns out that at full tilt boogie, the compressor, fan, and water pump pull 2.9kW. This lowers the cost-per-hour to $0.1531, making it an incredible cost savings over gas. In cold weather, most heat pumps switch over to electrical resistance heat. An equivalent amount of resistance heat to our 3-ton heatpump is 10.5kW meaning a cost of $0.5544/hr. Most folks without gas end up in this situation. Why don’t we? Our heat pump is ground-coupled, also called geothermal or ground-source. What we have is a 1200′ loop of pipe buried 6′ down that we circulate water through. At 6′ down, the temperature is near 60F year round. Instead of trying to extract heat from cold outside air in the winter, we can pull heat out of the ground all day long. In fact, most heat pumps will quit working and switch to electrical heat in cold weather simply because the outside unit will move its heat into your house, condense water, freeze it and promptly quit working. We have a similar advantage for summer cooling – we can pump heat into the dirt instead of trying to get rid of it in 90F air. And there’s no ugly box outside the house.

We’ve told people building new houses that they should consider ground-source. So far, they haven’t. They also have higher utility bills.

Hey Good Lookin’, Want to Contango?

bryan — Sun, 21 Jan 2007 18:35:52 +0000

Odd sort of word, isn’t it? I came across the term while doing a bit of comparison shopping. Just to warn you, for most, this discussion is about to get tediously boring. What I wanted to do was compare the cost of heating our home with the heat pump we have to an equivalent amount of heating derived from natural gas. The caveat here is that I don’t know exactly how much electricity our heat pump pulls, but a generous and probably high guess is 6kW. Electricity costs us $0.0528/kWh, making our cost to heat (or cool) $0.3166/hour.

The heating/cooling capacity of our heat pump is 3 tons. This is pretty normal sizing for medium sized houses. 3 tons of heating works out to a rate of 36,000 BTU/hour. Natural gas is priced per thousand cubic feet (Mcf)*. At 80% efficiency, one Mcf of natural gas releases about 1.049 million BTUs when burned. This means that an equivalent amount of heating consumes 0.0342 Mcf per hour. According to DOE resources, in October 2006, residential natural gas prices were running about $12.74/Mcf. At that price, it would cost us $0.4372/hour to heat.

With the demand for heating at 5 hours a day during an cold month, that $0.1206 per hour difference could cost us an extra $14.95.

Anyway, back to contango. It isn’t, as my previous use would suggest, a verb. It is a term used to describe a situation in futures trading when the price for future delivery of a commodity is higher than the spot price. It is a normal condition arising from the fact that holding a non-perishable commodity generally costs something to the holder. That commodity you have to deliver in the future ties up storage space and the costs involved are figured into the futures contract. It is the price to pay for the guarantee that the commodity in question will be available when you need it without you having to store it. If, on the other hand, you can buy the commodity on the spot market and store it more cheaply than the party you’d be making a futures contract with… well, you do the math.

* Yes, I am well aware of the fact that abbreviating “thousand cubic feet” as Mcf is completely counterintuitive. It is, oddly enough, a Roman numerial type of deal with ‘M’ standing in for 1000. “Hundred cubic feet” is thus abbreviated Ccf. The same applies to BTUs: MBTU is actually 1000 BTUs. One million is, thusly, MMBTU. I don’t make this stuff up.

Man of Science, Man of Faith » Heatpump

Recount

Hey Good Lookin’, Want to Contango?