09042010

Global Warmings unscientific method

There seems to be a lot of interest in using heat pumps (aka heat exchangers as found in air conditioning units) to replace traditional hot water heating methods (like an electric heater or gas). They are even being presented as possibly more efficient than a solar hot water heater...

The Cost of running a heat pump

Most heat pumps for the purposes of heating hot water seem to be rated around 1.3Kw - assuming a duty cycle of 33% (i.e. in operation for a third of time) and using a typical pricing model for water heaters of 11.3 cents per Kw. One gets a yearly electricity bill of around $285 attributed to the running cost of the heat pump alone. Now on the face of it this sounds great. But be aware the compressor is warranted for usually around 2 years max and the tank around 5years max. So if one assumes over 20 years that you could be up for replacing the compressor once every 4 years or so that's 5 compressors you would go through - not sure of the exact cost of this but lets put that at around $1500. The water tank should last maybe 10 years - so replaced once over 20 years - say another $1500.

So over 20 years - the heat pump would cost you in total (20 * 285 + 6 * 1500) = $14700. Add to that the installation cost and you get upto $18700.

Or look at this another way your current way of heating water would have to cost you more than $935 per year for a heat pump to be more cost effective.

So why the push for heat pumps?

I think this is simple really, they attract the same number of REC's as solar plus are easier to install and initially a cheaper outlay. But as we have shown over 20 years solar is more reliable and cheaper to run.

The Cost of running a solar water heater

The running cost of a solar water heater is usually in the circulation pump (if you have one). That's around 0.03Kw (30 watt) an hour. Assuming it runs half the time (dark at night) - that is an annual cost (on the same pricing model above) of $30. Now solar panels are usually warranted for 10 years (if you get a good one). So expect to be replacing that once in 20 years - circa $3000 I'd say. The circulation pump is around $300 tops and  would be replaced every 5 years tops. The hot water tank should last the same - so $1500 over 20 years.

Total cost over 20 years is 5000 + 30 x 20 + 3000 + 1500 + 300 x 4 = $6300

Or look at it another way your current way of heating your hot water would have to be cheaper than $535 per year to be more efficient.