Your refrigerator is probably a much bigger electricity user than all of these. It’s running all the time, maintaining about a 40ºF difference from room temp. (And people keep opening the door, letting the cold air escape. (Even standing there just looking, with the door open. A friend who has several teenagers has said that replacing his refrigerator with a cooler that has clear glass doors, like those in grocery stores, would probably cut one third off his electric bill.)
How about looking at it thermodynamically? Mixing hot and cold could power a heat engine and do work. This means this system is doing extra work (or producing too little entropy?) I think the most efficient way would be to set temperature as low as possible so that you use up all your hot water every day.
A big efficiency problem with water heaters is the varying and unpredictable demand for hot water. The common household water heater is a dumb device. When hot water starts flowing it has no idea if you’re washing your hands, running the dishwasher, taking a shower, or filling the bathtub. And it has no prior warning of when those things will happen. In addition to that, it can’t control the amount of water that it heats. All we need to solve this problem are water heaters that can vary the volume of the tank, and read our minds.
Your tank would loose heat overnight, and the heating coils would consume more energy to keep it hotter overnight.
You unfortunately would not save energy by keeping the temperature hotter, but you would have more hot water available at the proper temperature by mixing it with the cold water. The key is more hot water means more energy used.
If you have an electric water heater and a fairly regular hot water use schedule, you could save money with a water heater timer. Water has a large specific heat capacity, which means it cools off really slowly. Back when I was working, my water heater was set to two hours on in the morning and two hours on in the evening. I had all the hot water I needed for a long, hot shower in the morning- the evening cycle provided for the more sporadic laundry and dishwasher use. Since water stays hot a long time once it’s heated, I had plenty for hand washing, etc. all day long.
We dealt with a simar issue recently with hot water, and I just wanted to mention that many plumbers recommend you heat your water to at least 140 as to prevent legionnaires bacteria from growing in the tank.
having an anti-scald value at every faucet/shower would be needed.
You fridge really shouldn’t be running all the time unless it’s got some insulation or seal issues. Your AC system, OTOH, has a much, much bigger compressor, bigger evap motor, bigger cond motor and your house is insulated so much worse then your fridge it’s not even comparable. (Unless you have one of those super new houses with expanding foam insulation, triple pane vinyl windows, doors with perfect seals etc.)
A few years back I went from living with my AC on to making use of the ceiling fans I had in all the rooms and opening up windows. I found that since I was gone during the hottest hours of the day, all I had to do was open the windows when I got home and put a fan in the window to draw in the cool air since it was now dark out and the sun was down. Going from running my AC all summer to running it only on the hottest days (or when it’s too humid out, which makes the house clammy), my energy bill dropped nearly a hundred dollars a month. I, honestly, couldn’t believe what I was seeing. I thought I was reading the bill wrong or that something else was at play. My bill was nearly cut in half, but, doing some Googling, it seems that’s about what central air costs to run for a month.
My fridge is 6.2 amps or 744 watts. Even if it ran at full capacity 24 hours a day (which it doesn’t and that’s out of the scope of this thread), that would cost about $40 per month to run.
Programmable thermostats can save a load of electricity with heat pump systems. Many households have no one home for eight or more hours per day. Having the heat or A/C off then can really save a bundle.
Your hot water tank, like your thermostat, can benefit from a setup where the energy used is reduced when the service will ot be in demand - i.e. stop heating/cooling the house when nobody is home, and stop heating the water all day or all night when nobody is home or nobody needs superhot - exactly as California J suggests. It does not take “more energy” to reheat the water than to keep it hot.
At the basic level, heat loss is generally proportional to heat differential and the quality of insulation. Letting water cool, say, 20F and then reheating after, it is less energy than keeping it at a very hot temperature for a whole daytime.
the heat lost for an hour when the water is 110 is less than the heat lost for an hour when the temp is 140. the heat lost that allowed it to drop to 110 is less than the heat lost for the equivalent time sitting at 140; therefore replacing that heat will be less than maintianing the temperature.
the risk is, of course, that your timer does not know about every other Friday off or Teacher days, sick days, etc.
Dracoi, I don’t dispute the difference between ambient air and the tank is the driver in heat loss. However, unless you have a breeze blowing through the jacket of the tank, the outside temperature of the metal tank versus ambient air is what determines the amount of heat loss. keeping your hot water tank in a warm (air) place helps reduce heat loss; putting it in a cold place increases heat loss. Over time, yes, a small amount of heat each hour can add up.
Do this simple test: turn off your tank, and see what temperature it is at after an hour. Turn it back on, let it get back to temperature, and try 2 hours, and so on. This will tell you how good the tank is. (If you drain some water to check the temperature, it is replaced by cold water - so unless you have a thermometer right in the tank, you won’t get a correct reading by drawing from the tank each hour).
Anothr issue is electrical rates. If electricity is based on demand, then having your (electric) tank heat up again when everyone is getting home, turning up the AC and cooking dinner is probably not cost effective. Overheat it at 3PM and leave it off until 9PM?
I didn’t mean the compressor is running, just that the fridge is maintaining the temperature difference all the time.
This is the general idea of ‘tankless’ water heaters – don’t have a tankfull of water to maintain at a high temp; just heat water when hot water is needed. That requires a higher-capacity heater, but I expect that as water heaters are replaced, that will become the norm. We may even see 2 tankless water heaters in the house, one near the kitchen and one near the bathrooms, to avoid the loss of heat from long lengths of pipe containing hot water.
Also, remember that in places like here in Minnesota, for about 9 months out of the year, heat ‘lost’ from the hot water tank isn’t really lost – it goes into the house and helps keep it warmer. Not as efficient as a furnace, but not wasted energy.
For optimum efficiency, determine what the hottest temperature you need is from your hot water faucet, and then set your heater to that. So, for instance, if your highest-temperature use is the shower, then you should be turning on only the hot tap in the shower and not using the cold water at all, and that should be the right temperature.
This may have other consequences, like running out of shower water quicker. That’s the tradeoff against efficiency.