Yeah... that's how you get an average COP of ~3 throughout the year. Even cold areas have a spring, summer and fall. The COP is nearly 5 when the garage is ~90F. Why waste gas heating water in a warm garage AND curtail solar???
Why are you not supportive of electrification? A water heater is one of the best examples of 'value stacking'. Take something you need anyway and make it a 'battery'. Might only be ~3kWh but it's ~3kWh for the price of a wifi connection and some software. Can't do that if you're using gas.
Are you judging all HPWH from one bad anecdotal experience you had?
Aside from the GE Geospring most HPWH will run >10 years with no problems. It's just a refrigerator in reverse.... how much maintenance does your refrigerator need? As I mentioned previously if you're in an area with hard water they significantly reduce maintenance.
-
Because of what I see as you ignorance of the technical aspects of HP principles and operation, I believe you have no idea of the meaning or significance of what I've written with respect to HPWH operation in this or other threads. Therefore, I believe what you think of it's relevance makes little impact on it's accuracy.
The discussion did indeed begin about a device to add on to electric water heating methods. I'd note that the OP has a single post to this forum and so none since the original the first post to this thread.
The discussion, for this thread anyway, quickly changed to one of HPWHs and their efficacy in cold(er) climates. That direction was initiated by Peakbagger for HPWRs and NewBostonConst. as to their possible poor performance in cold climates.
I added nat. gas to the thread discussions because I believe it represents a commonly (but by no means universally) available, more cost effective and more reliable way to heat water for residential applications.
Continue to fix your HPWR's as you wish. Although that's anecdotal information and so of limited use, I'd think relying on the mostly common sense KISS principle to require less fixing with a simpler method if/when possible is better than more fixing of more complicated systems.
Gas fired domestic water heaters are indeed complicated - compared to some passive solar methods such as batch heating or other methods of heating water. But few situations being aa/nothing, most commonly available gas fired equipment for domestic water heating applications is less complicated than, for example, heating with wood or pellet stoves, etc. It's not all/nothing. My engineering opinion, FWIW, is that available gas fired equipment for heating domestic water is less complicated, more developed and so more reliable, less costly to acquire and, in cold(er) climates, less expensive to operate than most all HPWHs in the same service. Most all of that seems to be borne out, BTW, by nwdiver's link to the Bonneville study of HPWR used for residential water heating.
My acknowledged lack of experience with HPWH refers to the specific application of HP science and technology as it may apply to domestic water heating only. I believe my experience in heat pumps practical applications, particularly as a means of residential space heating is greater than yours.
I'm also pretty sure my technical knowledge of the thermodynamics of HP and refrigerator operation, and how the Thermodynamics, heat transfer and fluid mechanical aspects may relate to the practical aspects of space conditioning using refrigeration and HP equipment is such that I may well have forgotten more about the subject than you'll know for some time - if ever - but I'll leave that to other's to determine for themselves.
From where I sit and type, you seem full of anecdotal and what seems to be casual observational information with little background or explanatory information to back up what you write. I believe you believe what you write. I don't believe what you write adds much that's meaningful to the conversations or the body of knowledge.
But it's all about opinions and they're like noses - everyone has one and all of them smell, at least some of the time.
Take what you want of the above. Scrap the rest.
Mods: I'm, out of this thread.
Leave a comment:
-
The total cost to own needs to be considered when purchasing all HVAC and water heating equipment. The energy savings can be quickly equalized by just one repair. The high efficiency equipment initial install is generally much higher than the standard efficiency unit, add in the complexity of the electronics, increased amount of parts and the decreased total lifespan of the system and your savings will be less than you assumed. Expect to get 10-12 yrs if your lucky from your HPHW tank and refrigeration circuit if it is properly maintained and the water quality is within the " FINE PRINT" of the warranty. Warranties cover just the parts not the labor so if you happen to get a "problem" unit there will be negative savings. Some manufacturers really suck when it comes to honoring warranties.
Don't believe the marketing hype from the manufacturers, ask someone in the trade.Leave a comment:
-
Thank you for the link. After reading/studying it, I believe it seems to confirm/back up a lot of what I think I know, believe and write about the efficacy of HPWH, particularly the figures/graphs that seem to confirm the idea that HPWH performance where source temps < 40 - 50 F tends to roll off to < 2 or so rather quickly and therefore less likely to be cost effective in colder climates where, whether you and Ampster choose to see or believe it or not, a good portion of the U.S. and the world happens to live.
I'd suggest you and others read it after you educate yourself about heat pump operation. If you do choose to educate yourself and then read you linked report, you may well agree that it confirms what you don't seem to currently agree with.
I'll leave this thread with the probably futile hope that both you and Ampster stick more to what you might know and look at things in a more detached way instead of parochially and often ignorantly relating anecdotal information as fact. Some of what you both sometimes write is interesting but IMO only, it's often wrong (such as the way you treat excess production payments to PV owners), or what you bloviate about simply and often misrepresents realty. I don't believe such behavior is in the best interest of the goal of providing as accurate information as possible, if that's part of what's supposed to happen around here.
You two fit more into the AZWS crowd. Too much of the "I did/read/heard this once, it agrees with what I like and so it must be true" (non) logic with little to back up beyond what seems to me to be mostly ego and ignorant opinions.
Take what you want of the above. Scrap the rest.
Leave a comment:
-
Only true nowadays. In the past, the simple pilot light and millivolt thermopile to control the gas valve, was good for the life of the heater (10 + years). I've seen the modern components fail in 2 years. The glow coil ignitor on my home furnace would last 2 seasons max. The electronic brain in my Viking range, 3 replacements in the last 7 years.
Yet when I was growing up, I only recall the water heater being replaced once, and the furnace only needing new air filters. It's a poor trade off to get rid of simple, reliable pilot lights, and replace with electronics that fail. It may save a few therms over their being a lit pilot light, but the waste involved in manufacturing and disposing of glow coils and electronic control modules, is going to be a lot more, but shifted to a different country.
Leave a comment:
-
Most of what you have written may not be relevant to the original poster who linked to an Australian product to retrofit an electric water heater. If he is from Australia, and his heat source is electricity then it is likely that a HPWH will be more cost effective than a resistive element to heat water. The discussion began as a discussion about an electric water heater.
There is no question about the higher initial cost, but with a payback of less than five years the long term cost of operation is better than resistive heat. You can believe what you want about maintenance costs, but your lack of actual experience makes your argument resemble what I have heard from the Gas Company peddlers, which is mostly negative. Focusing on cold climates ignores the benefits provided in warmer climates. I will acknowledge that the Geospring has had some issues.. I fixed mine easily and the issue had nothing to do with the heat pump portion. It is still going strong. My other three units have had no maintenance issues. One is still doing well after 9 years.In any climate, I'd still take into consideration what I believe is the likely higher initial investment required for a HPWH as well as what I'd bet will be higher maint. costs and service requirements, and the intangible PITA factor costs that can come from violating the KISS principle by choosing more complicated HPWH over simple gas fired methods to meet a DHW duty.
There is nothing simple about gas fired water heaters either. I have had to replace control valves and igniters over the years. It is much simpler to design a home with a HPWH because there is no flue or gas line to run. They can be located in conditioned space and draw and vent air from where ever it is most efficient. Furthermore, I have not yet been cited by the KISS police for violating that principle. I did gain more room for panels when I eliminated the water heater vent on my roof.Leave a comment:
-
Nearly all? That is not the situation in all cases where I have deployed HPWHs. Three are in unheated garages and the fourth is behind a vented exterior door. In fact none of the homes I have owned in California have water heaters in the heated space. One modification I am thinking of making in my home is to use air from my attic which is typically warmer than outside ambient air.
The original poster has a resistive element water heater and that is the comparison that is most relevant to this thread. The advantage of HPWHs over resistive element water heaters still remains despite efforts to side track this conversation by making a comparison to Natural Gas.
Leave a comment:
-
Actually, that cost/therm in terms of electricity prices at $0.17/kWh = (100,000 BTU/therm/3,412 BTU/kWh ) * $0.17/kWh = $4.98/ Therm.
That cost then needs to be divided by the effective COP of any HPWH, however that's figured. That will give the cost of fuel for operation of the HPWH which is not the cost per therm based on per kWh costs of electricity.
Q: Are the 1,255 and 3,493 kWh figures actuals, estimates, or from where ?
As a first approx., for fuel cost considerations only, based on your provided costs, that would mean as long as the net COP of the HPWH stays above ($4.98/($2.44/ combustion. eff. of the nat, gas fired water heater )) = 2.04*(comb. eff.) or so for your application and situation, the fuel cost of operating a HPWH will be less than the fuel cost of operating a nat. gas fired water heater. So, if fuel cost is the only economic figure of merit, the less cost source is f(4 things): HP heat source temp., electricity cost, nat. gas cost and nat. gas combustion eff.
In a warm climate such as yours, I've little doubt that a HPWH may well be more fuel cost effective than a nat. gas fired unit.
Most of what I've written in this thread pertains to HPWH operation and applications in cold(er) climates.
In any climate, I'd still take into consideration what I believe is the likely higher initial investment required for a HPWH as well as what I'd bet will be higher maint. costs and service requirements, and the intangible PITA factor costs that can come from violating the KISS principle by choosing more complicated HPWH over simple gas fired methods to meet a DHW duty.Leave a comment:
-
-
That's usually but not always the case. In such cases where the HP source for the heat is the conditioned air that's just been heated by nat. gas, a lot (but not all) of the sting is taken out of what amounts to putting a HP between a better/cheaper/faster energy source (nat. gas) and the DHW load.
If the HP source is outside air, the HPWH COP reduction will reflect the colder source temp. when the outside amb. air is colder than the air in the conditioned (and assumed heated) space. In such applications, one cheap and dirty, back of the envelope way to readjust the COP at the conditioned space heat source temp. accounting for a lot of the heat actually coming from fossil fuel combustion is to reduce that HP COP by 1/(furnace efficiency). So, a COP of, say, 4 with a 70 F source temp. and a furn. eff. of, say, 70 % becomes 4 - (1/0.70)) = 4 - 1.43 = 2.57. Depending on the outside air temp. that may actually still be above the HP COP if/when outside air is the heat source, particularly if/where coil defrost is part of the cost considerations.Leave a comment:
-
-
I just returned from 3 days in Alaska, with no Internet access, to see this discussion continues to rage on.
Using the numbers that J.P.M. articulated above I was pleasantly surprised to see that my substitution of a HPWH for a 10 year old rusted gas water heater was actually better than I thought. My lowest cost rate for electricity is $0.17 per kWh. Using the example above that brings my cost per therm to $1.75 compared to natural gas at $2.44 per therm. Obviously everyone doesn't enjoy my low rate (EV-A from PG&E).
However when it comes to comparing HPWH to a resistive element water heater., the HPWH uses almost a third less kWhrs in a typical year. (1255 kWhs vs 3493 kWhs).Last edited by Ampster; 08-07-2019, 11:10 AM.Leave a comment:
-
Point being that $0.35/kWh is near the highest rate that anyone in the country will pay for a kWh (not to mention ~3x higher than the US average) and this isn't about retail costs but using SURPLUS solar to heat water. Which goes back to my original statement of 'Most people in most places' very few people are paying $0.35/kWh, fewer still among people that have surplus solar generation...
In NM since I produce more than I consume using an additional kWh to heat water 'costs' me ~$0.024/kWh. Meaning the check I get from Xcel is ~$0.024/kWh smaller. At my rental in WA it's $0 since under PSE any annual excess is lost. So as long production exceeds consumption it literally costs nothing to heat water.
Beyond that not everyone has natural gas and it's increasingly falling out of favor. Berkeley recently banned gas for all new homes.
There's a wider context that you're ignoring. Electrification if done in a way that flattens the demand curve can decrease the cost of electricity because fixed costs become a lower percentage of overall cost. Water heaters are one of the cheapest ways to do this since they're essentially a 3kWh thermal battery. PLUS; the amount of solar generation we're losing due to curtailment is only going to increase; Why not use it to heat water?Last edited by nwdiver; 08-06-2019, 01:32 PM.Leave a comment:
-
For starters, I'll stick to how you incorrectly handle the savings by using POCO reimbursement rates and not discuss the relative merits/drawbacks of HPWH vs. nat. gas water heating.
I don't believe my use of the super off peak rate of $0.35/kWh from my POCO for power is disingenuous as much as it was quite conservative. It's the lowest rate available for a tariff most customers of SDG & E are on now or soon will be on using a T.O.U. tariff. Using the lowest rate assumes all water heating is done only at times of super off peak rates. While that's certainly possible, my guess is many or most residential users have no concept of what I just wrote, much less do it. If I had used some blend of hourly per kWh rates rates based on a more likely usage pattern, the cost/kWh would have been closer to something like ~ $0.40/kWh or so, making the more likely HPWH scenario I used even less cost effective compared to nat. gas.
Disingenuous: Not candid or sincere, typically by pretending to know less than one really does.
To my memory, your implication that I pretend to know less than I do will be the first time anyone's accused me of that behavior. Often, I'm considered at least a condescending prick, and a cross between a computer and a prostitute, that is, an f-bombing know-it-all, but that's off topic.
As I've not checked it, I accept your 200 TWH/mo. as excess, and even though I may not understand your reference and assume it has something to do with CA statewide excess PV production, but I'm not sure how much that has to do directly with the economics of residential excess energy production.
And, even though it's also probably off topic, I also disagree that increased electrification is always the best way to go. FWIW, the way I learned it many years ago, the better way to meet an energy need is to match the quality of the source of energy to the quality of the energy required for the task. Don't cut butter with a chain saw. Electricity is a very low entropy (very high quality) form of energy. That low(er) entropy and high quality gives it a lot of versatility. Example: You can heat water with electricity, but try directly powering the screen your looking at with nat. gas or wood. The nat. gas can be used to generate electricity at something like 40 % production eff. at a central generating station with the gained advantage of more flexibility of the product (the electricity put on the grid) to do more tasks than the nat. gas by itself. To then use that electricity to do something the gas could do directly (heating water) wastes that versatility and the money spent on the electricity generation.
Now, and more on the topic of your use of POCO reimbursement rates as a measure of cost effectiveness: Do and think as you want, NOMB or concern, but perhaps to help others not well versed in such subjects avoid thinking your logic is correct and to be followed, know that using the reimbursement rate of $0.05/kWh, or any reimbursement amount as a basis for costing as you have done is way off the mark and incorrect.
The correct number to use is the avoided cost of the electricity used to meet the duty required for the task. Reimbursement can improve the excess generation economics some, but usually only a little, and only fully when the reimbursement price/kWh == the cost of PV generation per kWh. That rarely happens. In the case of residential water heating using electricity, that cost will either be the cost of power from the grid, or the cost of PV generated electricity, or some blended mix of rates, not the reimbursement price paid for excess PV production.
To keep it simple, on topic and not muddy the waters, assume the cost per kWh of rooftop PV generated electricity is the same as the price paid for grid tied electricity by whatever costing method the party paying for the power chooses. Also assume a HPWH replaces an existing electric resistance tank type water heater, and the existing PV system exactly offsets electricity usage before changeout to a HPWR. Also assume that all other electricity uses remain the same, making the HPWR usage vs. the electric resistance heating the only usage change. The PV system also remains unchanged and is sized to meet the entire pre-changeout annual electrical load. I appreciate the system annual output will change, but for the sake of simplicity, assume it's constant year to year. If that's not acceptable use total modeled PV production for the system lifecycle divided by the number of years used in the lifecycle.
The HPWH will use less electricity to meet the water heating task than the old tank type resistance heater. So, for this example and conditions, the annual household electricity use will drop by an equal amount. That will result in an equal electrical bill (and because the PV is sized to replace the entire electrical load == $0 or some annual min. payment), but excess energy production will result in an excess production payment to be made at some low rate such as the $0.05/kWh you use. Keep the overgeneration payment separate from the electric bill for now.
Next, consider the cost per kWh of PV generated electricity. Say a system of 10 STC kW is in place, cost the owner $21,000 after tax credits and generates enough electricity to exactly meet the annual pre HPWH load as in the example. For reference, say that annual generation and annual use before the HPWH changeout is 16,000 kWh/yr.
The PV system was paid for in cash up front. It's a sunk cost and so cannot be recovered. The fact that it's a sunk cost is one key here. You won't get any of that money back by energy improvements.
The HPWH changeout will do nothing to reduce the annual cost of owning the PV system. Since PV generation already offsets 100 % of usage before the changeout, what the changeout will do is reduce the amount of the PV produced electricity that goes to offset (now reduced) usage that formerly carried a production value of the retail electricity rate and now has a value of $ 0.05/kWh. After the changeout, the resulting excess production is only gaining $0.05/kWh. Before the changeout, that production was valued at the much higher retail rate.
Look at it another way and still using my simplified example with some numbers using what I consider to be my genuous, conservative but still traceable and actual $0.35/kWh rate.
From the example, 16,000 kWh/yr * $0.35/kWh = $5,600/yr. annual production value and annual electricity cost with the result of a zeroed out bill. Now, reduce that annual load by, say, 1,000 kWh/yr. as a result of the changeout from electric resistance heating to a HPWH. The bill is still zero or some min. charge, but the cost of the PV system is unchanged (remember the sunk cost ?). So, for one thing, the benefit from the reduced usage is only the excess generation credit, but the $5,600- $300 = $5,300 net annual cost will lower the per kWh cost effectiveness of what's now effectively an oversized system. What's happened by the changeout is that, in effect, the system revenue has been lowered by ($0.35-$0.05) * 1,000 kWh/yr. = $300/yr. as a result of the underutilization of the now oversized system.
As an aside, that's also a way to see the wisdom of making as many lifestyle changes and energy improvements as possible before considering PV rather than after.
Although it may seem a bit like closing the barn door after the horse has gotten out, and without writing or implying anything about the economics of HPWH, and using the example's 1,600 kWh/hr. PV production per installed STC kW and $3.00 * 0.7 net installed cost/STC W, the system sunk cost could have been reduced by (1-(15,000/16,000))*$21,000 = $1,312 if the HPWH changeout had been done before PV was considered and the annual electric bill would still have been zeroed out. Perhaps coincidentally, I'd point out that $1,300 or so is in the neighborhood of the current material cost of a HPWH.
An analogy using fuel costs associated with driving an ICE vehicle: Say I buy a new car and plan on keeping and maintaining it for at least 10 years. I drive 30,000 miles/yr and my shiny new ICE vehicle gets 30 MPG. Also say gasoline currently cost $3.00/gal. I therefore will burn 1,000 gal. of gas/yr. at a cost of $3,000/yr. Now, my friendly gas station comes to me with a deal: For the up front consideration of $30,000, they will provide gasoline to me at the rate of 1,000 gal./yr. for the next 10 years. Anything > than 1,000 gal./yr., I pay the going rate. Anything less than 1,000 gal./yr., they'll credit me at the rate of $0.05/gal. with no yr./yr. carryover. I take that bet because, among other reasons, I feel gas prices will only go up. Now, about 6 months into my 10 year deal, I see an ad for a super duper add on to ICE vehicles like mine that will guarantee to increase my gas mileage by 10%. I check it out and it's a true and honest claim. I continue to drive 30,000 miles/yr. Q: how much do I generate in fuel savings per year by getting the add on ? Answer: Since I've already paid $30 large my savings will be Zero $$. Cost: The cost of the add on device.
Point for those considering PV: Do your homework before getting PV and keep sight of the goal of lowering the electric bill as opposed to getting PV for it's own sake or an end in itself, and get the costing right.
Take what you want of the above. Scrap the rest.Leave a comment:
Leave a comment: