Sunday, August 24, 2008

Electric Trace Heating For Domestic Hot Water Pipes?

Hot Water Temperature Maintenance Self-Regulating Heating CableMy apartment shares a central gas boosted solar hot water system with the rest of the block at "City Edge" in Canberra's Inner North. This results in low hot water bills and minimal green house gas production, but wastes water. Perhaps I should install Electric Trace Heating, which would increase the energy use, but lower the water waste.

Water is heated by a large solar collector on the roof and when the sun is not shining by a large gas burner in the basement. The water is continuously pumped throughout the building, so it is hot when it gets to my apartment. But then there are several metres of pipe between where it arrives at the apartment and the taps. About 4 Litres of cold water has to come out of the internal plumbing before the hot water reaches the shower.

My efficient Australian made "Ecoshower" shower head uses only about 7.5 litres a minute, or 22.5 Litres for a three minute shower. So the cold water wasted is increasing the shower water consumption by 18%. In the kitchen this is a bigger problem with many litres of cold water going down the drain before the hot arrives.

By the way, a
s a subtle reminder to only have short showers, I have set the bathroom "tastic" heater to turn off after three minutes. So you see the light dim slightly to remind you you have been in too long. This is done using a motion sensor/timer, so the heater comes back on automatically when you step out of the shower.

As well as wasting water, the cold water is increasing my hot water bill. There is a meter on the hot water pipe and I am charged for a share of the building gas bill, according to how much water is used. So I am charged gas use for the cold water coming out of the pipe, before the hot water arrives. In my case this might be as much as 50% of the cost.

Electric Trace Heating (also known as Heat Tape and Pipe Heating Cable ) uses a fat flat electrical cable with a resistive element built in, which gets warm when current is put through it. A length of the cable is taped along the hot water pipe, between the normal hot water supply and the tap. Insulation is then wrapped around the pipe, and the cable plugged into an ordinary power point. A few watts of electricity is used to warm the pipe (about 14 Watts per metre). The cable is manufactured from a material which automatically regulates the temperature, so having its own built in thermostat and is designed for a set temperature.

I saw Thermon’s Warmtrace System on display at the 2006 Canberra Spring Home and Leisure Show , but haven't seen it mentioned elsewhere. Presumably the element only draws maximum power when the water in the pipe is cold, so it would not add much to the heating bill (or greenhouse effect).

Heat Tape seems to be common in the USA for preventing pipes from freezing. has Heat Tape for about $4 per meter. But note that the anti-freezing tape may heat to a lower temperature than that needed for domestic hot water. Also the USA uses a lower voltage than Australia and US tape can't be used in Australia. Also many of the tapes do not appear to be self regulating: they have a thermostat installed somewhere along the pipe, which would be less able to regulate the temperature.

There are also some practical problems with the heat tape: you have to run it along the length of the pipes and so need to be able to get to them where they run through the walls. The tape needs to be carefully installed, following detailed procedures. Also there has to be a power point handy somewhere to plug the tape into.

So the questions I have are:
  1. Is heat tape used for domestic hot water in Australia?
  2. Is the saving in water worth the increase in energy use?
  3. How much energy does the heat tape use in actual conditions?
Another option would be to install small electric water heaters near the taps. These would heat the first few litres of water.

Of course this all assumes that there is a reasonable charging system is used for the cost of the gas used for hot water. At present most of the bill I get is not for the cost of the gas used, but a fixed minimum charge. As a result there is little financial incentive to reduce energy use. It would be more cost effective to disconnect the solar and gas system and replace it with a conventional electric heater. This would be bad for the environment, but cheaper to run, as there would be no separate gas bill with its high minimum charge.

One interesting possibility would be to replace the complex pumping system and gas booster of the central solar system with the heat tape. At present water has to be continuously circulated with a pump to have hot water available. The pumps do not use much electricity, but when the sun is not shining, it is gas heated water which is being circulated. If the tape was installed on the pipes, that would remove the need for the pumps. It may also remove the need for the gas booster. Electricity is more expensive and less greenhouse friendly than gas, but this is only needed as a supplement and might make solar systems more practical.

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