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I was asked to write this blog about naturally aspirated fossil-fuel water heaters in green retrofits as a response to a rather heated debate at the recent National Green Building Conference. The debate occurred in a class co-hosted by Peter Yost and Michael Chandler; in that debate, I stated unequivocally to “get gas water heaters the hell out of the house — they have no place in a green retrofit!”
Natural aspiration wastes a lot of energy
The efficiency of naturally aspirated water heaters range from 54% to 62%. Believe it or not, the 62% model is 15% more efficient than the 54% model, so until recently it even qualified as Energy Star! That is just one of many reasons why I don’t really pay too much attention to Energy Star, but that is another long story.
Without getting into a lengthy discussion of why naturally aspirated combustion water heaters are so inefficient, let’s just summarize by stating that they cannot be placed inside the conditioned area of the home unless they are in a “cold room” and unless outdoor combustion air is ducted to the room. That means that the residual heat off the water heater is lost — in other words, it cannot help heat the house. This means that at least 38% of the heat you have paid for is gone up the stack, contributing to global warming, air pollution, and whatever else pushes your buttons.
Electric heating is 100% efficient
By contrast, an electric resistance water heater can be placed in the conditioned area of the house — even underneath a stairway or another unusable area — and the residual heat will help heat the house at 100% efficiency.
However, during the cooling season, when you are paying to run the air conditioner, this extra heat is unwelcome. If you are in a climate zone that requires considerable air conditioning, this may not be a good thing. Please consult your NOAA charts on Heating Degree Days and Cooling Degree Days before choosing a water heater. In my Pacific Northwest climate, we have zero cooling degree days, so an electric resistance water heater makes perfect sense.
In a climate with an equal number of heating degree days and cooling degree days, the residual heat would be of zero net-use. If you have more heating degree days than cooling degree days, you would receive a proportional benefit.
Coal is on the way out
OK, now you may argue that an electric resistance water heater may be fine for me, since I live in the land of hydroelectric power — clean energy and all that. But what if you live in a state powered by coal?
Coal-fired power plants are only between 30% and 40% efficient, and they emit all kinds of nasty stuff into the air. Agreed. But the reality is that coal-fired power plants are basically maxed out, running at full capacity just to supply the current loads. Nobody has any plans to build any new coal-fired plants to supply any new loads.
Were you listening to the President (I didn’t ask if you liked him — just if you were listening)? He stated unequivocally that he wants to tax coal-fired plants out of existence. You might not have believed him — after all, he didn’t get the cap-and-tax bill through Congress — but he is already starting to achieve his goals with regulation.
In Washington State, we have one coal-fired plant, located in Chehalis. Our governor has just brokered a deal that will take all coal units off-line by 2025. Those units will be replaced by clean-burning natural gas-fired plants at the same location, presumably using the latest and most efficient technology.
New natural gas plants are around 55% efficient. That might not seem like much next to your condensing 95% efficient furnace, but if you produce the electricity with natural gas, and then use a heat pump to heat your home, the heat pump will be around 300% efficient, depending on the model and your climate zone. Multiply the 300% by .55 (the efficiency of the power plant) and you will be around 165% efficient, or nearly twice as efficient as if you had used the gas directly in the home!
The grid ties us all together
If you live in the Deep South were most of the electrical load is met by coal, and if you are talking about an existing load on the system, you may have a small shred of an argument — until you consider that the entire electrical grid is tied together. As soon as you consider the fact that all electrical generation is tied to the same grid, and that all new loads will be supplied by natural gas, wind, or solar power, you will realize that when you are adding a new home to the system, that represents a new load, and your power is coming from a source other than coal.
The correct calculation to use when determining the efficiency of electricity vs. natural gas is as follows: Gas turned into electricity is about 55% to 60% efficient. Nationwide, line losses average about 6%, and 6% of 55% is about 3%. So reduce the “delivered to the house” efficiency of natural gas-fired electricity by 3%, to 52%. Multiply that by the Coefficient of Performance (COP) of your heat pump, or heat-pump water heater, and that is the net efficiency of your use of natural gas.
That would make a 225% efficient heat-pump water heater about 117% efficient, and your 300% efficient ductless minisplit heat pump about 156% efficient. You just can’t beat that using natural gas (or any other fossil fuel) in the home directly. (Your equipment is probably only listed by HSPF, Heating Season Performance Factor. To get COP, divide the HSPF by 3.412; since 3.0 = 300% efficient, an HSPF of 10.3 would yield a COP of 3.0.)
Focus on efficient equipment, not cheap fuel
Now let’s take a brief look at history: In 1974, the U.S. Department. of Commerce started keeping track of consumer energy prices as a separate component of the Consumer Price Index (CPI). In the last 37 years, the cost of energy at the consumer level has increased an average annual rate of 6.33%. If you are going to calculate the cost of the energy to run your new heating or water heating equipment, you need to factor in that inflation factor in relation to the life expectancy of the equipment — roughly 20 years. Energy that would cost only $30 today (a typical water heating bill) will cost $96 then. Worse, you will have paid over $13,600 for your hot water in that time. What if you saved 23% of that? What if you saved 47% of that?
Remember the numbers up above? The heat-pump water heater is about 117% efficient in its use of natural gas. That represents a savings of about 23% over an ultra-high-efficiency 95% water heater and a savings of about 47% over a water heater that is 62% efficient. If you chose the heat-pump water heater, you would have up to $6,400 to invest in your local utility company stock instead of having blown it up the chimney!
Finally, don’t pay too much attention to the price of natural gas today compared to the price of electricity today. These price relationships can change rapidly. When I built my commercial center ten years ago, heating oil was only 79 cents per gallon, so I put in oil-fired boilers. Boy, was I dumb!
Be smart: go with the units that use the least amount of fuel, not the lowest-price fuel. The price will stabilize over time. All energy is worth the same cost per therm or BTU or KWh, or whatever other unit of measurement you want to use. Save the gas for uses that require portability. Since your house stays in the same place, tie it to the grid.
Much of the discussion at the class mentioned in the first paragraph was related to how indoor air quality issues are affected by combustion appliances and energy retrofit work, especially air sealing measures. By the time the discussion was over, it was clear that no-one present could justify using naturally aspirated fossil-fueled water heaters in those conditions. I hope this article will persuade you that there are no conditions, anywhere, ever, that would justify their use.
Ted L. Clifton is a designer, a builder, and the founder of Zero-Energy Plans in Coupeville, Washington.
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43 Comments
energy sources
I believe your statements about energy sources are incorrect. In fact, there are dozens of new coal plants currently being built as well as a couple new nuclear plants. And if you assume that there may be a push to move away from nuclear, there is a possibility that even more coal plants will get built just like Germany has announced following its decision to shutter their nuclear plants. Energy policy is highly political so I think you may be jumping the gun in claiming that natural gas, solar, and wind will provide most of our energy in the near future, let alone within the lifespan of a water heater. Additionally, the grid actually is not all interconnected so whatever mix exists, does not necessarily exist in all regions.
Also, your calculations above don't seem to account for the costs of the new systems or equipment that would need to be purchased in order to reap the increased inefficiencies you pointed to. I don't believe these costs would wipe out the savings but they would come right off the top and reduce the savings and should be accounted for.
Overall, I agree and think we should plan for the future but we should also be realistic about what will and will not be happening in the next years and decades. Electric water heaters may also be attractive to those who produce their own electricity just as on demand heaters may be attractive to those with other constraints or designs.
Bad Advice
Unless you are willing to shell out big money to buy a water heat pump (and big money to repair it, due to its complexity), switching out your natural gas water heater is a BIG mistake from a monthly bill point of view. Keep in mind that any heat pump has a compressor, 2 coils, cooling fan, computer controls, etc, and it will likely cost as much to fix as when your central AC system goes out. And unlike central air, the water heat pump will be running all the time- 12 months a year, 24/7. The flip side of electric, electric resistance heat, is terribly inefficient and the most costly way to heat anything.
And environmentally, a natural gas water heater is the clear winner. Brian m is right. Today, nearly 60% of our electricity comes from coal and ONLY 1 to 2% from wind and solar. The idea that this will change significantly in our lifetime is misguided. Wind power is economic only because the wind power people get tax breaks and subsidies. Solar is not economic period, if you are talking photovoltaic; solar thermal is an option, but we are talking HUGE scale plants and few are stepping up to build them. We will be lucky if in 2050, wind and solar make up 10% of the mix.
And...although I think natural gas turbines are a very environmentally friendly way to generate electricity, it must be mentioned that significant losses are associated with the transmission and distribution of electricity. Whenever you convert energy from one form to another and transport it over a distance there are efficiency losses. Buy a modern, clean-burning natural gas heater and you will be ahead both economically and environmentally.
There are also direct vent
There are also direct vent gas hot water heaters, with much lower standby losses.
And on demand hot water heaters.
And boilers that are 95 percent efficient that can be hooked to indirects.
Yes natural draft gas hot water heaters should go away, but not if favor of electric.
I did look though, and the heat pump hwh available online are not THAT much more than direct vent gas..........
Energy sources
To Joe: while you are correct in stating that at this time solar/wind are not economical compared to the current fuels, they would be if 1) they were not subsidized by our tax dollars and 2) if the true costs of burning coal were directly associated with the current pricing. As a nation, we "subsidize" these industries twice- once with direct subsidies from our tax dollars and again cleaning up the environment (how do you restore a mountain top?), health care costs associated with dirty air/water. If the true cost of burning coal was directly linked to the price of the electricity produced, the alternatives would not only be competitive, some may even be less expensive. All of this means that electricity will be more expensive in the future which is why conservation will become a much more important aspect of the equation.
speaking of bad advice, joe's
speaking of bad advice, joe's claim that natural gas water heater is the environmental 'clear winner' is incorrect if looking at source energy (which we should be if we're talking about environmental winners)... natural gas may be 'clean burning' (only because all the nasty stuff is flared out further up the pipe) but it's far from 'clean'.
on the projects we're working on, the source CO2 emissions for high efficiency natural gas and electric water heaters are consistently higher than a HWHP.
Serious bias from the NW
It sure seems like your analysis rests heavily on generous accounts of heat pump COP in varied climates, and on very generous source energy assumptions for electricity. I agree, atmospherically drafted water heaters are stupid, stupid devices of a bygone era, and the suggestion that we let their combustion by-products heat the home "passively" is just plain dumb. It is just as smart as "heating" your home by cooking with unvented gas in the winter. Yes, it heats your home, and yes, it poisons you and your loved ones. BUT you are in a tough position, as a professional from the Northwest. Don't tell a customer in CA, who is paying tier 3 or 4 electrical rates on their now peak-load-inflating electric water heater that the prices they are facing are soon to fall, just because rates are so absurdly low in your own region. Although, at $0.30 to $0.40 per kWh, solar PV starts to look really nice on a $/kW basis...
I have questions, too
I believe that some of Ted's figures seem to be skewed to favor his position.
I think a more realistic figure for the efficiency of natural gas generation plants is 43%, not 55%. (Source: http://www.npc.org/Study_Topic_Papers/4-DTG-ElectricEfficiency.pdf).
The average COP of in-service heat-pump water heaters is closer to 2.0 (source: http://www.wapa.gov/es/pubs/esb/2008/aug/aug084.htm) than 2.25. (Manufacturers often underestimate the use of electric-resistance backup elements.)
The average COP of ductless minisplit air-source heat pumps is probably about 2.3, not 3.0. (Source: Andy Shapiro, https://www.greenbuildingadvisor.com/blogs/dept/musings/heating-tight-well-insulated-house ).
@Josh- You are right that a true cost analysis needs to be
performed to really understand and argue cost comparisons and therefore future costs and benefits. The fact is that we pay one price at the gas pump or on our utility bills and additional costs in our taxes. The costs we pay on our utility bills do not fully account for the true costs. Even the true direct costs of fossil fuels aren't accounted for there. The cost of finding, extracting, processing, transporting, regulating, waste management, etc. are not reflected in our bills. if we were to assess all these costs for all the different types of energy resources, we would see that renewables/sustainables are actually more competitive than we are currently led to believe. This is also the extent of analysis that would better guide congress and governments on investments than the hired hands and shills currently pulling the strings.
Sorry about the rant ; ) perhaps another post to discuss the future of energy policy would be informative since people are attempting to predict the future of energy resources and the equipment and investment that may come as a result?
Taking your own advice is a good idea!
Joshua you bring up some good points; I mostly agree with you.
Now Mike has got some good advice too, and he should take his own advice- look at the source energy. No offense Mike, I liked your snappy comeback :- )
Natural gas is the cleanest burning fossil fuel with the least CO2 output. It comes out of the ground, does not require refining like oil does (no waste left behind), and with no or almost no treating goes into a pipeline in TX or LA that ends up at your house. Losses of natural gas along the pipeline are less than 1%.
The losses to transmit electricity are about 7% to go a much shorter distance. And in a nation where 60% of the power is generated with coal, the fact that coal puts out much higher CO2 than natgas is only the “tip of the iceberg,” so to speak.
I’m talking about the poisons in coal- mercury, arsenic, sulfur dioxide, etc. Years ago, it was so bad it would burn the paint off cars (remember acid rain?), think of what it does to people.
My gripe with the article is that it goes nation wide, and in a nation where coal is the biggest power source and getting bigger, it is still BAD ADVICE.
two issues
There seems to be a lot of confusion -- or at least I get confused as I read the arguments, both in the article and in the responses. Maybe the math sorts it all out better than logic, but I don't think so ....
logically, there are two separate issues involved and by mixing the two the conclusions seem sometimes arbitrary and sometimes just ... confusing.
One issue is public policy ... energy generation. It is political of course, and a matter of business/economic history and investment, and the issue is also climate dependent and geographically resource dependent. A generalization about any "solution" that doesn't account for these variables is unwise, doomed, or both.
The second issue is extremely local -- the production of DHW in my house. That's not possible to determine with glossy generalizations. Because of my own experience -- in central MA (oil country) and now in north GA (heat pump heaven) -- I'd wonder why anyone would suggest anything but solar. But then, I wouldn't know if that shoe would fit other people, other places, ....
Perhaps frustration lets us oversimplify what is truly complex ... not beyond understanding or solution but surely complex.
Joe too
Use more gas...
Darn it.... I knew I would miss a good brawl with Yost and Chandler in Utah. I would like to propose to use more gas appliances. If so, it would allow Mr. T. Boone Pickens to make more money, so he can donate more to Oklahoma State football... go Cowboys!!! ;-))
You guys all make me smile!
I have enjoyed every comment above. Most are very good, a few demonstrate that you didn't really read the whole article...
Regarding Martin's numbers on gas-powered generation plants, he is referring to the full existing stock, which includes some units built a hundred years ago. I was referencing NEW LOADS, which require NEW SOURCES of POWER. The newest generation of gas powered turbines is delivering electricity at 59% efficient (Seimens) and General Electric is touting a new unit that will achieve greater than 60% efficiency.
That having been said, the heat pump water heater is not the right tool for every location, but it is certainly the right tool in California, and any other hot climate. Have you considered that with the heat pump water heater installed inside the conditioned area, you will be air-conditioning the home as you heat the water, using the same energy? How COOL is that? And, as one of you mentioned above, the heat pump water heater is about the same price as a power-vented gas unit, and is cheaper to install. It is way cheaper than most on-demand units.
The homes we are building now are entirely solar powered, using zero fossil fuels and are powerful enough to supply enough surplus energy to power the owners electric car. Who says there isn't enough sun in the Pacific Northwest? Cost effective? You bet, the homes we are building come at a premium over our competitors of about $75,000, but they will save the owner more than $350,000 over the life of their mortgage, when you add up the cost of fuel for the car and the house.
But then that is a story for yet another blog...
Very interesting dicussion
I will keep my opinion short:
#1 Electric resistance is a bad idea (Reasons given above)
#2 Heat pumps make sense if combined with the heating system (justifies the price)
#3 Efficient natural gas systems make sense especially if the infrastructure is already there
After all the hot water production makes up a pretty small amount in traditional construction. In low energy houses this topic is very interesting and I would probably shoot for #2 or invest in solar thermal. For retrofits #3 is definitely worth considering.
An example
Here's an example of how keeping the focus on one level at a time of the public policy - commercial - individual energy demand relationship leads to real creativity and possible long-term solutions.
http://www.ecobuildtrends.com/2011/06/concentrated-solar-power-csp.html
Enjoy.
Joe
Robbing Peter to pay Paul?
To me it has always appeared that the problem with heat-pump water heaters is that they take heat from the ambient air in the house. In the winter time the heat is most likely to come from the a gas-fired furnace which begs the question "what are the efficiencies for first warming the air with gas and then using that heat to warm your water?" I have always assumed that it would not be worth the cost. If your calculations are correct, however, a heat pump water heater would indeed make sense during the winter since the efficiency calculation becomes: Gas-to electricity (52%) X heat-pump-water-heater (225%) X gas furnace (90% my house) = 105%. During the summer it should help cool the house.
Jay has it right... almost
Jay has done the correct math here, but imagine how efficient the heat pump water heater would be if your were heating the home with a heat pump? As I said yesterday, the heat pump water heater makes the MOST sense in a cooling climate, where you will also be cooling the house using the SAME energy.
The real key to this whole argument of gas vs electricity is that we DO have the capability to develop 100% of our own renewable energy, whether it be through PV, solar hot water, or wind. If we continue wasting our natural gas resources heating homes and hot water, we will not have it for powering truck, trains, and eventually airplanes. Using 100% electrical energy to operate a home makes perfect sense, in this context.
My own home is down in the trees, there is no way I can get PV or wind, but I am able to design and build homes nearby that produce more energy than they use. They supply me (indirectly through the power grid) renewable electricity, and my trees eat up some of the carbon our cars are still spewing out on a daily basis. In other words, none of us are perfect, but we are all striving to get better at what we do, and how we do it.
A little more information on Electrical Rates...
According to the NPC report Martin Holladay referenced in his response to my article above, the Advanced NGCC (Natural Gas Condensing generators) as of 2005 (six years ago) were producing electricity at about 54% efficiency. When you consider the price of one therm of Natural Gas (about 100k BTU), and factor in the 54% efficiency factor of these units, the utility companies are able to produce electricity for just under .08¢ per KWH, if they were buying their natural gas at current retail prices. They are not.
Those of you who are promoting the use of natural gas for heating or water heating in the home (unless you are in a VERY COLD climate, where COPS of heat pumps drop dramatically) have been drinking the Energy Company's kool-aid too long! Utility companies are regulated, the electric companies are the most heavily regulated. Who are the regulators? WE ARE! If your electrical utility is ripping you off, or making bad decisions about how to generate electricity, whose fault is that? it is YOURS! GET INVOLVED! Public energy policy is YOUR POLICY!
When you take the 54% efficiency from the 2005 study up to the 60% efficiency claimed by GE in their newest units, and then consider that the utility companies are probably buying their natural gas at less than half of the retail price, you can easily see that it will probably cost them less than .03¢ per KWH to generate electricity using this new equipment. I recall seeing a report from GE that claimed less than .02¢ per KWH!
I am not an expert on the cost of turbine generators, but I would bet my bottom dollar that if you add up the cost of purchasing and installing all the individual gas-fired units in every house that would otherwise be served by such a unit, it would far exceed the cost of the generator. Then add up the cost of maintaining all those individual units over time, and you will find that the new condensing turbine generator is a very good buy indeed.
Gas water heaters
Why is the US not like so much of the world where they have solar hot water heaters? They have come way down in price. Then there are direct vent on demand heaters like I have, that also is connected through a heat exchanger and heats all the radiators in my house.
If the US is switching off dirty coal, then it is going to hydraulically fractured natural gas, burning it to boil water to spin a turbine to turn a generator to send electricity over a wire, losing a third of it on the way to...boil water? That's just crazy.
Get rid of gas water heaters
As has been stated direct vent gas water heaters negate the first objection. They are 95% efficeint and use natural gas, which is the largest untapped energy source in the US. Now if you have a heat pump HVAC system a desuperheater connected in-line with the water heater provides free hot water in summer and some hot water in the winter. The gas system is used as a backup and topup system. This I believe is a very efficeint hybrid system. We have also fitted a direct vent gas dual fuel HVAC system for the same reason.
Response to Lloyd Alter
Lloyd,
1. "Why is the US not like so much of the world where they have solar hot water heaters?"
A. Solar water heaters have been available in the U.S. for over 100 years.
2. " They have come way down in price."
A. Really? What's your source? Copper is way up. It's really hard to get a solar hot water system installed in Vermont for less than $8,000. A much more typical price is $10,000.
As a consumer, I am not
As a consumer, I am not particularly motivated by what happens "upstream", I make decisions based on the cost-efficiency, to ME. Looking at my latest bills, I am paying $0.18 / KWH for electricity, and $1.34/Therm for Gas (plus a $10 minimum charge). I believe a therm is equal in energy to about 29.3 KWH, so gas energy costs roughly 4.5 cents/KWH, 1/4 of electricity.
If the electric heater is 100% efficient (seems high - the spilled heat is welcome only half the year, in these parts) and the gas unit is 50% (below your reported 54-62%), electric still costs TWICE as much as gas, to do the same job.
Are there distortions in the pricing structure? Sure - as a society we should be pricing/taxing carbon-based energy to multiples (like 5x) of the current price. Pollution (at the source, the conversion to electricity, and the end use) should be included in the economic costs, so it can play a part in my decision making process. But we as a society have decided yo take a different route.
I am not interested in paying double to heat my water next year, based on math/logic that I cannot follow, and fuzzy predictions for future prices. Even if all externalities could be factored in, gas is probably still a better deal than electricity.
(comment edited to remove blooper)
No gas? Works well in the UK
I support Martin Holladay's observations that the grid is likely to be far dirtier than suggested by the article. Over here in the UK (coal power stations being 33% efficient and *new* gas power station being 55% efficient) we fnd that the Primary Energy ratio is about 2.7, so the system efficiency is about 37% (1/2.7=0.37).
Good - room sealed with balanced flues etc - condensing gas boilers have a measured efficiency of about 93% efficient (you can see report suggesting 110% as they use a different datum when including for benefits of condensate.) Rounding things off a little at 90% efficiency it can be seem that they use 1.1 units of primary energy for every kWh of heat (1/0.9=1.1). In terms of primary energy for a heat pump to break even with gas you therefore need a seasonal COP of 2.45 (2.7/1.1=2.45). Similarly with CO2 the UK grid is 0.57 kg.CO2/kWh whereas gas is 0.194 kg.CO2/kWh. If in terms of carbon emissions you want to break even you need a seasonal COP of 2.93 (0.57/0.194=2.93, 293%).
Assuming that ALL power stations in the USA (or state depending upon how your grid works) are using NEW gas turnbines - no coal, at 40% efficiency, including 6% distribution losses, that is a primary energy factor of about 2.5 (1/0.43= 2.5, 250%), then you need seasonal COPs of over 2.27, 227%, if you are to break even with half decent European gas heating technology (I've ignored control systems that can improve the functional efficiency even further). In terms of capital cost gas boilers are cheaper than heat pumps (at least that is the case in the UK.)
From this quick and dirty analysis I can now see that some - though not all - of Martins more realistic COPs appear to just start to break even in the USA - assuming that they are seasonal COPs and not "when performing under test conditions." Domestic hot water is generallyt the Achilies heal of heat pumps.
How does this exersise work with energy costs?
heatpumps MOVE heat not create it
I'm amazed.... I'm no engineer but I do know that HEAT PUMPS MOVE HEAT NOT majically CREATE IT!!! With that said how are you heating/cooling your house? now you need to add that into all of your silly equations. Oh ya, are you dumping the cold air by product outside??? if not then you need to pay and use fossil fuels to heat that air and you only moved the heat from the room to the tank. If so, CFM in CFM out.. what temp and humidity is the air you are sucking in?
HEAT PUMP manufacturers clearly LIE (maybe it's not clear and that's why the "experts" believe them) when they state these COP's!!! Do you see mini-split air conditioner compressors in the house??? Of course NOT because you are dumping the heat (or cold) outside the space you are trying to condition while extracting energy from the OUTSIDE, NOT THE INSIDE and Not keeping it in the Same space!!! The key thought here is using/moving energy from outside, whether it be air to air, ground source, water source... if you see the common thread hear... they are all OUTSIDE.
Please correct me if I'm wrong. But I must say that felt kind of good though. Thanks for getting my heart rate up... I think I needed that. Check out this site: http://www.toolbase.org/Technology-Inventory/Plumbing/heat-pump-water-heaters
Every climate zone has its own requirements
Jim Olsen only has half the information he needs to get his heart rate up that high. If you are in a cooling climate, you would want to put your heat pump water heater inside the conditioned area, to help cool the home as it heats the hot water. If you are in a moderate climate, like 2/3 of the population centers in the US, you would put the heat pump water heater in the garage, where it can draw from air that is typically warmer than the outside air, but it won't hurt to draw that temperature down a few degrees.
My personal favorite is the air-to-water heat pump, which heats both the house and the domestic hot water, from the outside air. They are listed with COPs ranging from around 2.7 to 3.5, depending on the brand, but this is at the average ambient outside temperature, in my area that is about 47 degrees. The warmer the outside air temperature, the higher the COPs. In Florida, for example, the same unit might have a COP around 4.0, whereas in my neighborhood it would be about 2.7.
We are doing solar hot water here for between 5k and 7k, depending on the size of the system.
Even if the heat pump is only marginally better than the direct use of gas in the home, it is still better, because you can use PV panels to create the energy you need to power it. You cannot in any way EVER replace the natural gas you use. Once you have used it, it is GONE! When are you nay-sayers going to GET IT?
Water Heaters - Gas vs Electric
When we moved into this house it had a gas fired, 38 gallon water heater.
It ran ALL the time and provided an inadequate amount of hot water.
For $300 I exchanged it for a 52 gallon electric water heater on a timer.
The timer is on for 2 hours in the morning and 2 hours in the evening, the rest of the time it is off and costing us nothing and we have plenty of hot water all the time. We use about 125-140 gallons per day except for laundry day and just my wife and I live here. The electric bill went up a little but the propane bill went way down.
Exactly right.. it depends how you use it and how you augment it
The Manufacturers sell these like they have a Static COP but as you know the COP is very dynamic and depends heavily on the ambient conditions and building type the heat pump is located. Stick it in one 10x10 room and it has a COP of 1. Stick it in another 10x10 room and it might get a COP of 3 depending on how it was installed.
I want to see a closed loop system between my refrigerator and my water heater... one place I want heat and the other I want cooling... when you sell that I'll listen.
The general public can't figure out if it's what's best for them so they hire you to help them decide and what do you say??? It's 300% efficient when that's a bunch of crap!!! it's probably based on a constant of 75 degree ambient air... if that thing is running alot in the winter it's going to freeze out a space and if it's super humid in your house, like portland, 50% of the energy goes down the DRAIN as condensate now your 200% efficient water heater is back to 100%... Ambient temp and humidity.
Naysayer... I'd say Pragmatic. My job is to bring ALL of the information to my clients not just a blanket COP
Your PV panel doesn't select which appliance it powers and if you are suggesting that they should be sold as a package then do it.. it will only retail for $15,000.. at this point I'd rather own a NG micro CHP where everything is on demand.
Stop selling the false promises (that heat pumps have a COP of 2-4 and taking advantage of the uninformed public! I want to see the COP curve for an outdoor unit in multiple climates with multiple configurations not in a conditioned space where the ambient temp is 75 degrees with 10% humidity... and I want to see how it effects the energy load of the rest of the home. They work great where you live in the world of $.05 kwh hydro and you don't insulate your home... but not so much in NY or Minneapolis.. or Denver. It's an expensive "you might realize a savings but there is no way to document COP with all of the variables, but just trust me on this"...
It comes down to "it depends" not "they have a COP of 3" in all climates and all installations. The rest is just jibberish
Lets get some facts straight!
Mr. Naysayer is getting a little hot, isn't he?
To start with, we have more heating degree days here than in New York City, where all the people are located. Everywhere else down the Eastern seaboard has even fewer HDDs. Furthermore, we have ZERO cooling degree days here, so your will experience higher COPs with an air-to-water heat pump in NYC than we will experience here. We pay about .10.25¢ per KWh here.
We have documented the savings, not by comparing a before and after change-out, but by out-performing the HERS rating for the whole house. We have never had to change out a gas water heater in any of our homes, because we never made that mistake in the first place. Our promises are not false, they are well documented, and much appreciated by our customers.
I am not advocating using hot water heat pumps in all locations, under all conditions. My article is intended to get you to think about your use of energy, and how to use it more efficiently. If you don't "believe" in heat pumps, perhaps the tooth fairy can help you out!
One of our homes, in Eastern Oregon, has been proving the efficiency of ductless mini-split heat pumps at very low overnight temperatures. In the first TWO months of operation (February and March 2011), the 1000 sf house drew only 276 KWh from the grid during the overnight hours. During that period of time, the AVERAGE nighttime lows were 20 degrees F, with many nights down around zero. Some of this energy had to be used for lighting and cooking, which just helps to demonstrate how a properly designed home, with the right equipment, can be really thrifty on the pocketbook.
Jim, I absolutely agree with you on the Refrigerator to Water Heater connection, that is a product I have been begging for for years. It just makes perfect sense. Now if we can just figure out how to cook with a heat pump...
viewing the math
There's a lot of comments here on which numbers are relevant to use and who has the right ones. There are supply side #s, consumer side #s, efficiency #s, actual or assumed energy rates, inflation, rising energy costs, annuity, etc, etc. Its a common issue to a lot of discussions on GBA. Does anyone have some simple(!?) spreadsheets where these #s can be made plain? It would be a great topic/project for someone with the knowledge and time to them up, so as to compare various systems.
It depends
It depends. Thanks for the friendly banter! no gas to the house can eliminate the service charge from the gas company as well.
The other thing to consider (from a cost point): 1kwh=3413btu's=$.10=34000 btus per dollar...... now 1 therm=100,000 btus=$.80= 125,000btu's per dollar x 90% efficient h2o heater=112500btu's per dollar... now if I did my math right you would need a COP of 3.1 to break even with natural gas... I don't see those things running at a steady 3.0..
I take 1 minute showers, my wife takes 2 minute showers, and the kids take 20 minute baths.. usually we try to time it with the sun because we have solar hot water. Use little, need little. Now lets get into Fracking... just kidding.
When it comes down to it I agree with you that.... well I'm still the naysayer. Thanks again for the discussion.
Nice price on natural gas
I notice Jim Olsen is getting his natural gas for .80¢, yet Curtis Betts, the consumer above, is paying $1.34 per therm. I have been using $1.25 for my calculations, though the most recent price around here has been $1.30. At $1.20 per therm, Jim's natural gas starts getting expensive at a COP of just 2.0. Even the worst heat pump will beat that, and the better ones will beat that down to about 5 degrees F.
Christopher Vicek has the right question, unfortunately the spreadsheets are not simple. I have dozens of them, each one for it's own circumstance. I create a new one for each house, each situation, and sometimes I even change that one three or four times, considering even things like tax liabilities, before finally recommending a specific product to my client.
I have submitted another blog, which I hope will be published soon, that deals specifically with the investment side of the energy equation. Stay tuned to this channel....
One more thought...
Does it seem to you like perhaps the energy companies are manipulating prices, to convince you to purchase the equipment they want you to use? Why would natural gas be just .80¢ in one part of the USA, and be $1.34 in another? Gasoline at the pump has far higher transportation and handling costs, and it only varies by a few cents from state to state, mostly having to do with tax rates. I'm just saying...
Useful Spreadsheet
You can access a very useful spreadsheet, called the ZEP Energy Cost Calculator on my web site, http://www.zero-energyplans.com. I designed it several years ago for calculating the relative cost of heating the home with various fuels and equipment efficiencies, but there is no reason it would not work for water heating equipment as well. You will find the link half way down the Home Page, in the left hand column. Enjoy!
Your calculator doesn't tell the whole story
Your calculator wasn't that clear to me... I'm simple. Once again if you live in a cold area (like you mentioned above) then these things don't work. If you live in a hot area and use the heat pump for cooling they work but I'd stick a black tank on the roof if I lived in a hot place. What are the assumptions with the COP... what testing conditions did they use to arrive at this #? Figure it out and let me know so you can change the naysayer to a believer.
Heat pump COPs
The US Department of Energy sets the standards by which heat pumps shall be tested. The air-to-water heat pumps I use list different COPs for each temperature range, in approximately 15 degree increments. For example, at 10 degrees F, it has a COP of 2.1, bringing the water up to 120 degrees. at 17 degrees outside temperature, it has a COP of 2.2; at 33 it is 2.5; and at 47 it has a COP of 2.8. At 55 degrees, the COP jumps up to 3.1. Since our average outside temperature is about 49 degrees on a year 'round basis, this unit will heat domestic hot water at a COP upwards of 2.8. I rate it for home heating at about 2.7.
The ductless minisplit heat pumps i use list their COPs at various temperature ranges also. These ranges seem to correspond to the design degree temperature in the different climate zones. I am in Zone 4, so my COPs are higher than for homes I have designed in Zone 5. I don't have these numbers stored on my computer, and I am on the road right now, but I can assure you that they are above 3.0 for outside temperatures in the high twenties, around 2.8 for temperatures in the teens, and still above 2.0 for temperatures even below zero degrees F.
The US DOE does not allow them to measure any type of heat pump at part-load conditions, the fact is that this type of system is even more efficient at part-load, so reality will provide a result better than the advertised number, since most heating equipment is virtually always running at part-load conditions. I have been using these systems for a couple of years now, and we have the results to prove it.
Shall I leave a dime under your pillow?
COPs of HPWHs
Ted,
The COP of a heat-pump water heater as measured in a lab underestimates the use of the electric resistance backup element. In a real family, during times of heavy water use, the electric resistance element comes on, dragging down the COP.
The only way to honestly measure the in-service COP of a HPWH is in the field, in a real home, over the course of a year. This has been done many times, and the results are usually in the 2.0 range, but are sometimes much lower.
COPs of HPWHs
Martin,
The system I described above is not your store variety HPWH. The units I use have no electric back-up, and they have a capacity of about 140 gallons per day. The key to avoiding the electric backup is in the storage capacity, for which we use two 50 gallon standard electric water heaters, without the electricity turned on. In case of system failure, the electricity is connected to the second tank. For a very large family, the second tank could also provide the extra boost for peak periods, and that would bring the COPs down as you suggest.
Split HPWH will trump
Once the split system HPWHs become available, then they are the obvious best choice. Their operational cost should be competitive with gas in most markets.
hot water heating
I'm ignorant about all this important domestic infrastructure, but (I forget whose) suggestion about connecting the heating power of a fridge to a water tank got me wondering. In a place like Vermont, could you run tubing behind the refrigerator coils, almost touching them, circulate the water from a storage tank through the tubing to pre-heat the water, and then use one of those point-source electric resistance shower-head water heaters that works so well in warm climates to give you hot-tish showers?
Are there any good, simple, straightforward guides (with lots of pictures) to these systems and how they work, out there?
Thanks guys.
Response to Lydia
Lydia,
Q. "In a place like Vermont, could you run tubing behind the refrigerator coils, almost touching them, circulate the water from a storage tank through the tubing to pre-heat the water, and then use one of those point-source electric resistance shower-head water heaters that works so well in warm climates to give you hot-tish showers?"
A. Yes, but such a system wouldn't raise the temperature of the water very much, because your suggested method won't result in efficient heat transfer. For better heat transfer, you'd need a device engineered from the start to be a dual-use appliance. One problem: the refrigerator's compressor operation doesn't coincide with hot water demand.
gas water heaters
Lots of good ideas here, though it sounds like there's no perfect solution. Direct vent GWH's address a lot of concerns, and are affordable. it maybe should be pointed out that the more you reduce your hot water consumption, the less these efficiency comparisons matter. Got teenagers? Consider a coin-operated shower! And one other reminder - if you're fortunate enough to have natural gas at you home, you can use itwithout adding additional load to an electric system already struggling to figure out how to pay for additional generation infrastructure. Using existing infrastructure has obvious economic advantages for ratepayers, and probably for the planet as well.
Electric Heat Pump HVAC System recommendation ?
Hi Ted, I attended and enjoyed your presentation regarding Ballard's first Zero Energy House. I am presently remodeling my 1950's brick veneer house here in Seattle (consists of main floor with basement - roughly 1200 sf ea) ... to become an all electric solar house with Solar PV (great exposure). Insulation will be R 34 walls, R 60 attic. Dbl pane windows .3 U. I am considering electric ductless heat pump for heating and a electric heat pump water heater. Is there a heat pump product you would recommend that would heat both domestic water and house? Thanks.
Response to Vic Opperman
Vic,
There is at least one device that does what you ask -- the Altherma from Daikin.
Prepare to open your wallet, however. Two GBA readers have shared information on the cost of an Altherma system. Mike O'Brien was quoted $22,000 to install an Altherma in his house, while Nick Lehto was quoted $36,000 to install an Altherma system in his 1,800-square-foot house. Big numbers.
Heat Pump Water Heater choice
Vic, for the Ballard house we used a UniChiller from Unico. It is thousands less than the Daikin, though you do need to add a separate water tank with a coil in it, but it does basically the same thing. The UniChiller heats up water to about 125 degrees, and feeds it to a buffer tank that stays between 115 and 125 degrees, depending on where it is in the heating cycle. The in-floor radiant system draws directly off the buffer tank to supply water to the floor loops, this is tempered with a tempering valve to keep the water in the floor to around 90 degrees. This can be adjusted as necessary, keep it as low as will do the job. The tank with the coil in it also draws water through the coil from the buffer tank, using its own t'stat to operate its own circ. pump. The in-coming domestic hot water is then heated by the coil in that tank to between 105 and 115 degrees, again depending on where you are in the heating cycle. The average 110 degree water is then sent to the electric hot water tank, which only needs to bring the temperature up a few more degrees, if at all. The owners of the Ballard house have found that they never run out of hot water, and 110 degrees is hot enough for showers and any other normal domestic uses.
The efficiency of this system comes from two sources:
1. Since the outside air temperature in our area averages 50 degrees over the course of the full year, the average efficiency of the UniChiller is about 300%. The system will run at more than 200% efficient right down to about 10 degrees, which is colder than it normally ever gets here.
2. Since the ground water temperature averages around 50 degrees, the in-coming domestic water is heated up an average of 60 degrees by the 300% efficient UniChiller, and at most only another 10 degrees by the electric hot water tank. This means that about 86% of the water heating is done by the 300% efficient system, and the other 14% is done by the 100% efficient system (our stand-by losses do not count for this discussion, this replaces a portion of the space heating load). On average, then, this system is about 272% efficient on a year-round basis.
The proof is in the actual energy use of the house, it is below what the HERS rating predicted by a considerable margin, we will not know the exact numbers until we have a full year of energy use data. Suffice to say, we will be way below net-zero with the 6.44KW PV system.
We used a similar system for another house near Coupeville, it has an average monthly utility bill around $30, including heat, hot water, cooking, everything, it is an all-electric house, with no alternative energy systems employed.
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