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From: ark@alice.UucP (Andrew Koenig)
Newsgroups: net.consumers
Subject: Re: Heat pump/water heater energy conservation
Message-ID: <4696@alice.UUCP>
Date: Thu, 12-Dec-85 18:39:30 EST
Article-I.D.: alice.4696
Posted: Thu Dec 12 18:39:30 1985
Date-Received: Fri, 13-Dec-85 20:34:46 EST
References: <237@neurad.UUCP>
Organization: Bell Labs, Murray Hill
Lines: 43

Well, I can talk about water heaters anyway:

> Finally, with regards to the hot water heater, is it advisable to install a
> timer so that it only runs when people are likely to be home.
> In other words, is the energy needed to reheat the water more or less
> than that required to maintain the water temperature for a prolonged period of
> no hot water use. My hot water usage is quite modest, yet I think this
> appliance is quite an energy hog.

Electric heaters are essentially 100% efficient.  In other words, all
the electrical energy you buy goes into heating the water.  Once the
water is heated, some of that energy leaks away -- through the walls
of the tank, through the pipes, and so on.

Given that you do not change your hot water usage, the ways to
reduce your electric hot water bills are:

	1. reduce the amount of energy that leaks away.

	2. reduce the energy rate you pay.

It may be possible to use a timer to achieve #2 -- some electric companies
vary their charges depending on time of day.

But what about #1?  Well, the amount of energy leakage is proportional
to the temperature difference between the water heater and the
surrounding air, multiplied by a constant that measures the efficiency
of the insulating barrier between air and water.  Thus, if you
lower the average temperature of the water, you lower your energy
loss.

In other words, to reduce energy leakage, you can (a) lower the temperature
of your hot water, or (b) improve the insulation on the tank.  Doing
both together, of course, works better still.

Since energy loss per unit time is linear in the temperature difference,
reducing the water temperature only while no one is home is indeed
a win compared with keeping it hot all the time.

Another possibility is to do what I did -- scrap the electric water
heater entirely and replace it by an oil- or gas-fired heater.  Buying
energy in the form of electricity is much more expensive than buying
it as oil or gas.