Peak Electric Usage

Many heat pump installations include an electric heating element in the air box for those days when it is so cold there is just not enough heat out th ere to pump. If it is turning that element on you are draining about as muc h as an electric furnace, which is substantial.

Many people are clueless about this happening if they are on a budget plan that averages out the monthly bill over year. It is nice to know what the b ill will be every month but sometimes you lack information on how much you actually use. hey might get a notice of an adjustment saying they will pay more in the next year but by then all that money is down the tubes.

The heat pump is just a compressor which actually cools the outside air. On e thing that could be wrong is a lack of efficiency causing it to run almo st constantly. Another would be some sort of clog in the refrigerant (seale d system) that would make the motor pull more power. Both are unlikely. If you have 240 volts running to the air box inside, more than likely it has a heating element in it and that is where the power goes, especially peak po wer.

And of course the old clogged condenser or evaporator

That may be true in lower latitude countries where solar heating is a problem but it certainly isn't true in the UK. Consumption here peaks at about 6pm in midwinter and is a flat minimum from midnight to 6am.

Here heating is entirely unnecessary in summer and cooling is only needed on a handful of unusually sunny days. You can count on the fingers of one had the number of such days per year.

Why are you aggressively heating the house in the middle of the night?

Perhaps enough people use oil CH or allow their homes to cool a little overnight. It seems overkill to heat a house when everyone is in bed!

Air-to-air heat pumps are quite usable with outside temperatures between -10 C and +10 C. Below -10 C the usefulness is questionable and below -20 C more or less useless (just an expensive electric heater :-).

That 12 kW sounds a lot if it is the average for several hours and not from a peak reading meter. That would indicate a very large house or badly insulated house.

If the outside temperature often drops below -20 C, I would suggest installing oil filled electric radiators in those rooms that are actually used during winter evenings and nights. The room temperature can then be set selectively for each room as needed and let the heat pump maintain say +15 C inside temperature in those rooms that are not actively used during the night. This reduces the peak demand and also reduces the heat pump wear.

Yes, I'm aware of the different heating requirements in Europe. I had a co nversation about electricity usage with someone from Germany about this onl y to realize that they don't heat with electricity at all because their req uirements make heat pumps entirely impractical.

To keep from freezing to death. As someone else pointed out the most commo n backup heat for the heat pump is straight resistance heating which has no efficiency benefit. That is why the electric meter spins like a top at ni

ontinue to work well at lower temperatures but maybe I am kidding myself.

colder should I let it get at night?

Rick C.

air box for those days when it is so cold there is just not enough heat out there to pump. If it is turning that element on you are draining about as much as an electric furnace, which is substantial.

That makes no sense. It is a max of 12 kW during the night when the electr ic coils run as backup heat. Whether it was an average or a continuous rea ding makes little difference. The electric company gives a total usage in graph form either by the month, day or hour of kWHr. I was looking at hour ly data where kWHr/Hr is kW.

There may be some small benefit to this, but when the rest of the house coo ls over night and then had to be heated back up the next morning the result ing savings is much less than you might expect. The only savings would be due to lower heat losses from the lower differential temperatures which at

emperature precipitously which would put pipes at risk of freezing. Pipes are often in places that are closer to the outside temperature than the roo m temperature and can freeze if the room temperature drops much below 50

iginal pipes were run in the outside wall to the kitchen sink. I had to ri p up the garage ceiling and move them into the undersink cabinet space so t his wouldn't repeat. But even now if the temperature gets much below 50

don't want to have to remember to do that *every* night.

Rick C.

Please note that the energy policy in Europe varies greatly from country to country.

The Germans and Danes are shooting themselves in the foot with their renewable only policy. France has a surplus of nuclear energy, Norway runs entirely on hydroelectric, Sweden and Finland on both hydroelectric and nuclear.

In Finland, new houses have been heated since the 1970's mostly with direct or indirect electric heating, now often with heat pumps. In addition to air-to-air heat pumps,"geothermal" ground or ground water heat pumps are often used using the energy from last summer stored in the ground or ground water. Drilling a 100-200 m hole is often enough.

I would have expected that to happen at -10 or -15 C.

Look for _reliable_ COP (Coefficient of Performance) figures for _your_ heat pump at low temperatures. Sooner or later COP drops to 1.

You sleep quite well in such _air_ temperatures. If it feels too cold in the evening, using electric blankets or radiation heating makes life comfortable.

If you only have peak power issues a few days a year, why do you insist of returning those rooms to "normal" temperatures each morning?

I have heard of stories of water pipes _outside_ the building,but then I thought this must be n urban legend, but then I heard of some cases in UK, but I would't have expected that such stupidity is also possible in the US.

Also in a lot of European countries they run large underground insulated water pipes from the thermal power stations to blocks of houses, and in winter rather than dissipating the ~ 65% waste heat of the power station in cooling towers, they pump it to heat the houses instead. That makes a lot more sense than wasting ~65% of the thermal input from the fuel in a cooling tower, though I imagine it might be problematic when the thermal power stations get shut down.

But you first said summer.

People come home from work in the late afternoon. Then they start cooking, turning on the A/C, run the washer and dryer. Well, at least government folks with easy jobs. Engineers get home at 7pm or later :-)

The A/C is the heaviest hitter in power consumption during summer and those things easily draw 5-10kW per residence. Even people who come home later have the A/C on a timer so they do not return to a sweltering house. Mostly this is archaic technology and power consumption could be greatly reduce but neither industry nor government understand this.

How could power consumption be reduced? Better insulation? Reflective coating on windows? Plant shade trees?

On Monday, April 2, 2018 at 2:09:37 AM UTC-4, snipped-for-privacy@gmail.com wrote :

e afternoon. But looking at my hourly electrical usage over the course of the year, it is clear the peak residential usage for anyone with a heat pum p is in the winter at night. My peak usage during the summer was less than 4 kW in any given hour. My winter peak was more like 12 kW and run like t hat from 7 PM to 11 AM. I saw this on six different days this season.

, but it sure seems like the difference between 4 kW and 12 kW for all thos e heat pumps would make a big dent in the power supply. Are the other usag es of electrical power really that shut down on winter nights so that summe r day usage is dominant?

Your heat pump is undersized. The thermostats makes the decision to turn on the auxiliary electric heat, usually when the measured indoor air temperat ure falls below 3oF of the setpoint, which means the heat pump can't keep u p. You might invest in better insulation and air sealing your abode, and th en decide if you need to upgrade.

... and after the houses, the water flows into tubing under the sidewalks before returning to the power plant :-)

This keeps the sidewalks free of snow and ice and very cold water enters the steam turbine condenser, creating a better vacuum and hence increasing the turbine Carnot efficiency by maximizing the temperature difference between the hot and cold side.

Realistically this requires a sufficient price difference between electricity and district heat. In addition, keeping the sidewalks dry requires quite a lot of tubing, so I have seen this usage only in city centers.

When using expensive fuels, you try to get out most of it. For example first run it through a gas turbine, then run exhausts through a boiler, run a steam through a steam turbine, use some of the steam for district heating and sidewalk heating and the sidewalk water for steam condenser cooling. Combine this with district cooling, there are many ways to optimize the primary energy usage.

Or simple PV solar panels.

In this case the production and consumption matches well. No need for batteries or grid connection, simplifying design and construction,

at

a conversation about electricity usage with someone from Germany about thi s only to realize that they don't heat with electricity at all because thei r requirements make heat pumps entirely impractical.

here the power plant, cement factory and trash incineration plant all contribute to the district heating

the power plant is ~47% efficient making just electricity, ~90% doing electricity and heating

The problem is that they still have to run when the electricity can bought cheaper from other sources

The new datacenter Apple is building is also going to add to district heati ng

The most drastic reduction occurs when switching to an evaporative cooler. Our regular central A/C draws around 7kW, the evaporative cooler I installed draws less than 10% of that. This is huge.

For people not liking this sort of cooling method you can change the design of a regular central A/C until so the outside condensor coil sees cooler air from an evaporative pre-cooler instead of the full 110F outside temp.

Of course, this only works in not so humid climates but that is a lot of the US. California, Arizona, Utah, New Mexiko, and so on.

Were we allowed a tax write-off for the evap cooler? Nope, of course not, because bureaucrats simply don't get it. You can get one if you buy a new central A/C with a slightly higher SEER number that saves 15% energy but you cannot get one if you installed a cooling system that saves 90%+.

We have a large older house with single pane windows, and a rather excessive amount of window area. Plus powerful pool pums that must run at least 4-5h during summer months to prevent the pool from capsizing towards algae pond status. Yet we regularly receive a notice from our utility that we are super low in our electrity use, in summer better than the average high-efficiency new home.

Resistive heating, of air or water, is crazy inefficient. And expensive.

Would that increase the humidity in the house? I guess that would be ok in dry climates. Not so good in Boston or Miami.

The increased humidity should help also.

Strange. They are trying to get you to use more electricity?

Yes, it increases the humidity and one has to account for that. For example by not setting a cold glass of beer directly onto untreated expensive would. There will be condensation and that can cause a water stain.

In Miami such cooling won't work but in Phoenix it does. As a country we should be smart and promote it where it works. This includes the correction of tax incentives.

No, it's a kudo email that we regularly get. For water use it still comes in the mail with the bills (we are also very low there).

What they did after lots of people spent money to switch to LED lighting was they ... jacked up the cost per kWh.