Hot water tank power saving?

[beaumeri]

Hi,

I was reading some folks are using the ELK-9200 Relay box to power down their hot water tank during the day to save energy. I taught the idea was great and I bought all the hardware for it.

Then while discussing with a friend he told me it might take more energy to bring the water tank back to normal temperature then to leave it running all time.

I was thinking about shutting down the power to the tank when we leave the house and power it back up 30 minutes before we get back from work.

What's your taught about this?

 

[fwd03]

If you have a good quality water heater, the heat does not escape much.
We brought a top of line GE water heater. Even during gas burner working full blast, it feelss cold outside.
If your water heater is electrical, heat element is on demand. If nobody using hot water, it does not consume energy.

 

[apostolakisl]

Hi,

I was reading some folks are using the ELK-9200 Relay box to power down their hot water tank during the day to save energy. I taught the idea was great and I bought all the hardware for it.

Then while discussing with a friend he told me it might take more energy to bring the water tank back to normal temperature then to leave it running all time.

I was thinking about shutting down the power to the tank when we leave the house and power it back up 30 minutes before we get back from work.

What's your taught about this?

Your friend is wrong. It takes more energy to keep it hot all the time. The amount of energy extra is a factor of how quickly heat escapes the tank. In other words, how well insulated is the tank and what is the temperature of the room you keep the tank in. Also, is the tank inside your home? If the tank is inside the home and it is ac season, you are getting a double whammy as the heat escapes into the house and then you have to cool it. If it is heating season, the loss is minimal becuase it is just going to help out the furnace.

 

[Desert_AIP]

Electrical water heaters are very efficient and well insulated. Plus it's easy to add insulation like a disk of 2" foam on top.
Chances are the heat lost during the day is not much more than the hysteresis settings that trigger the element to come on anyway.
So killing the power during the day may not do anything.

Turning it off during an extended period, like a vacation, IS a good idea. So it is proably worth it to set the system up to control the heater. Automating it during Vacation mode can save electricity, but more importantly will automatically turn it back on when you get home. Helps avoid cold showers the next morning!

 

[Sandpiper]

Heat loss from a full tank and no water flowing is proportional to the difference in temperature of the hot water and the ambient temperature. The RATE of heat loss is dependant on the amount and type of insulation. So if you let the temperature of the water cool off, the heater will consume less power. Heating the water back up after it cools off is power you would have used anyway if the water were kept at the higher temperature- it is just used at a later time. So the savings in power results solely from the lower temperature and how long you let it sit there.

 

[apostolakisl]

If your water heater is electrical, heat element is on demand. If nobody using hot water, it does not consume energy.

The heating element in a standard (with tank) hot water heater is not "on demend" in the typical sense of "on demand". "On demand" hot water systems refer to ones where there is no tank and the water is heated as it is used. If you have a tank, you don't have one of these. If you have a tank, and it is set to 120 degrees, it will keep the water 120 +/- at all times regardless of whether anyone is using it or not. It will use more if people are using it as fresh cold water enters the tank when hot water is let out. Unless the hot water tank is in a 120 degree room, if it is on, it will use electricity.

FYI, "on demand" electric water heaters are not common and some power utilities won't even let you have them. While on average they use less electricity, when they are on (how water is being used) they require huge amps which means a larger service panel and large load fluctuations which the power co's don't like. Gas "on demand" units are very common, I have two of them and they work very well.

If you are curious to know how much shutting down the tank saves you, you could put an electric clock onto the power going to the heating element (use a relay). Let the tank get up to full temp and click off. Set the clock to 12 and note the real time. Let it sit with no water usage for say 10 hours. Check to see how many minutes the tank ran during those 10 hours by seeing how many minutes ran off your clock. Then, on another day, let the tank come to full temp, shut it off. Then 10 hours later, turn the tank back on and see how many minutes it takes to get back to full temp. The difference between those minutes and the minutes from day one is your savings.

 

[beaumeri]

My Water tank is a brand new top of the line 60 gallon GE unit. I guess it's well insulated and it's sitting inside the house sitting on radiant concrete floor. So based on the previous answers there is not much saving to do on the water tank...

 

[apostolakisl]

My Water tank is a brand new top of the line 60 gallon GE unit. I guess it's well insulated and it's sitting inside the house sitting on radiant concrete floor. So based on the previous answers there is not much saving to do on the water tank...

I see that you live in Montreal. I assume you have the heat on for 8 or 9 months of the year. Any heat that escapes the tank is going to heat the home, which is usually happening anyway. So, for most of the year, the only loss you have is the difference in efficiency between the how water heater efficiency and your regular home heating system's efficiency. Resistive element hot water heaters as a group is your least efficient way to heat anything, but, all things considered you probably aren't loosing much.

I am a little surprised you don't have natural gas in Montreal.

 

[beaumeri]

I see that you live in Montreal.

I am a little surprised you don't have natural gas in Montreal.

Well I live right beside the Montreal Island. Ile-perrot top be more precise. I've been looking for natural gas for a long time but my neiborhood do not have it available.. I had to settle back for electricity for my house. Can't win them all!

But, I have everything ready for geothermal including concrete radiant floor heated with hot water. I'm just finalizing the house construction then I'll drill the wells for geothermal. I'm slowly getting there..

 

[apostolakisl]

Well I live right beside the Montreal Island. Ile-perrot top be more precise. I've been looking for natural gas for a long time but my neiborhood do not have it available.. I had to settle back for electricity for my house. Can't win them all!

But, I have everything ready for geothermal including concrete radiant floor heated with hot water. I'm just finalizing the house construction then I'll drill the wells for geothermal. I'm slowly getting there..

You should be able to share your hot water for domestic use with your geo-thermal hot water for radiant floor heating. This will give you a virtually endless supply and be much more efficient than resistance heating. I don't know the details, but you might be able to just circulate that same water through your hot water tank and turn off the electricity to the tank. And during the cooling season you can dump the heat that was extracted from the house into the domestic hot water (if you even have cooling). The geothermal guys have a name for this, it is called something like a "de-superheater".

 

[Desert_AIP]

Resistive element hot water heaters as a group is your least efficient way to heat anything, but, all things considered you probably aren't loosing much.

Actually modern electric water heaters are in the 75-95% efficiency range, whereas most gas water heaters are in the 50-70% range and the most efficient condensing or tankless gas water heaters are in the 80-90% range, at a premium cost.

Gas has faster recovery time, the energy source may be cheaper, but gas has lower energy efficiency because of design constraints dealing with the combustion exhaust.

 

[apostolakisl]

Actually modern electric water heaters are in the 75-95% efficiency range, whereas most gas water heaters are in the 50-70% range and the most efficient condensing or tankless gas water heaters are in the 80-90% range, at a premium cost.

Gas has faster recovery time, the energy source may be cheaper, but gas has lower energy efficiency because of design constraints dealing with the combustion exhaust.

You aren't comparing apples to apples here.

When they say a hot water heater is 80% efficient, that means that it is at 80% of theoretical maximum for creating heat out of electricity. A geo-thermal heat pump is a totally different animal. You are not using electricity to create heat, you are using electricity to move heat from the ground into the water. Depending on the heat source temperature (the ground) and the effiency of your heat pump system, you produce far more usable heat with the same amount of electricity. Compared to resistance, geo-thermal is probably going to use 1/4 the electricity.

And compared to gas, I don't really care to compare an electric hot water efficiency of turning electricity to heat vs turning gas to heat, I care about turning dollars to heat. And it would be a very rare situation that electric rates were so low and gas rates were so high that electric was cheaper. Usually gas is 2 or 3 times less, plus, as you mentioned, you get a much faster recovery time. Plus, with gas, you can do on-demand and use that hot water heater closet for something else.

 

[Desert_AIP]

We're off on a tangent now.
But you have to compare lifecycle costs including equipment, installation and operating costs to get a true apples to apples comparison.

If you define efficiency in terms of operating cost, dollars to BTUs, then you must define that.
The term "energy efficiency" usually describes the useful work obtained from the energy input.

Geothermal never enetered into until the last, but I'm willing to bet the installation costs weigh heavily in overall dollar to BTU system wide efficiency.
And then of course there's Solar...
And electric heatpump water heaters...

My point, there is much less standby loss (the OP topic) in an electric tank heater than a gas model because of the way it is constructed.

 

[apostolakisl]

I wouldn't say it is a tangent becuase it was in response to the OP's sharing of further info on his system.

The OP said he is going to install geothermal. So if geo thermal is going in, then it would make a great deal of sense to use that to heat the water in addition to the structure instead of resistance heating. Resistance heating is usually the most expensive possible way to heat something. It certainly would make no sense to put geo-thermal in just to heat domestic hot water.

Energy efficiency in the context of heating something, is energy consumed in the act of bringing that thing up to temp. Heat-pumps and especially geo-thermal heat pumps are almost certainly going to be the most efficient at that, regardless of whether you look at dollars or btu's consumed.

Considering where the OP lives and the fact that he only has electric available to him, the geo-thermal system is likely to be a very good investment. Payback time on the order of less than 10 years would not surprise me in the least.

 

[beaumeri]

I was looking for potential savings on my electric tank until I get my geothermal in place (Hopefully next summer).

Regardless of the cost of installing geothermal I believe there is some saving to be done there on the long run as energy cost will only rise with time..

Based on my initial survey I should pay off the geothermal investment within 16-18 years assuming the energy cost do not go higher..

In the mean time I'm trying with the automation tinkering to be as efficient as I can be.. Tinkering is fun.