Electronic Thermal Storage Heating System for possible condo application
Does anyone here have any experience with this system? One of our HOA board members is real hot about proposing this for our owners to install in our condos to replace the existing electric baseboard heaters. An electrician that he knows claims that he did this in his home and that this resulted in a 50% reduction in his electric heating costs. The units are room sized; they are basically electric heaters that heat a core of high-density ceramic bricks during the off peak hours then draw the heat from those bricks via a fan to heat the room on demand. The condos in question are not primary residences but are rental units located in ski country. Are these systems all that the manufacturers claim they are? While I am in favor of doing anything that could save us some money, claims of 50 % savings seem a little stretched to me. You know what they say about if something sounds to good to be true. What do you all know about this stuff?
This is the website for the system that they are talking about: http://www.steffes.com/off-peak-heating/room-units.html Any advice would be appreciated. Thank you.
Replies
You're right to be a bit skeptical. 50% savings is large. Couldn't go to your link ... says it's no longer good. Basically, though you are talking about a thermal energy storage (TES) device. Energy wise they are less effcient than other conventional heating sources. Potential DOLLAR savings will depend on the rate schedule. TES works on the principle of storing heat during the off peak period (e.g. night time) when rates are low and making that available for use during other hours.
They actually use more energy because of the inefficiency of 1) storing energy and 2) retrieving energy. But if the rate schedule is skewed toward having high rates during the day you MIGHT take advantage of it. However, if the typical use is 'ski all day and socialize at home in the evening', there will be little or no savings ... may be a bit the opposite.
While your board member is commendable for being an advocate of reducing costs, he may not be technically savy about the ins and outs of energy and energy economics enough to really be objective. If he was, he'd be able to explain exactly why he got 50% savings on his bill.
Clarification please
Energy wise they are less effcient than other conventional heating sources
the inefficiency of 1) storing energy and 2) retrieving energy
Where is the inefficiency?
They are inefficient at transferring heat to the storage device and storing it. Then they have an inefficiency of transferring from the storage device to the space. Compare that w/ e.g. baseboard heat where there really is no inefficiency of getting the Btus into the space.
Anytime you store energy to be used later will have a degree of inefficiency to it. So TES always is less efficient than using the Btus directly from the source (e.g. furnace or baseboard heat). The potential benefit is in the difference in the cost of the energy throughout the day (if there is one, but often w/ residential rate schedules there isn't, but it depends on the utility).
They are inefficient at transferring heat to the storage device and storing it. Then they have an inefficiency of transferring from the storage device to the space.
Oh? How? Where does the energy go to that makes them "inefficient"? Remember, efficiency is simply usable energy out divided by energy in. For something to be inefficient it must be losing energy somewhere.
Well you said it yourself, I think. The assumption was that the storage container was outside the house (although it may not have to be that, either). As you store the energy, there is loss in the storage unit. If you have to transfer energy to the storage unit from somewhere else (e.g. a hydronic piping loop to a boiler located somewhere else), you lose energy. You lose energy again to transfer it back to the house for practical use.
Some of these inefficiencies may be a wash w/ conventional systems (e.g. transferring the heat from the TES to the house). But ultimately, it's an energy loss, even if it be somewhat 'small'. The savings is in the rate schedule not in the efficiency (or maybe I should say 'effectiveness') of the TES.
Efficiency or effectiveness ... call it what you want ... the TES is inherently an energy loser. I'm not criticizing the technology, just stating the facts so a person can make an informed decision on whether it might be a good idea or not for their application. There is a time and place for just about everything. TES is a great idea for certain applications and can work very well to save some dollars.
Well, as I understand this particular design, the units are "room" units, actually in the rooms they heat. Any heat loss will be into the room that's targeted to be heated anyway. It's not "inherently an energy loser".
As you store the energy, there is loss in the storage unit.
True for energy, but not for heat. (There's a difference.)
Haven't read much on these
but here's what I think I understand.
Some of these are in-room units and as such would not lose any heat to the exterior.
There are a lot of larger units, and some of them might be outside the envelope. The electric utility here was pushing electric thermal storage boilers for a while, ideally to be used off-peak. They are/were fairly large, due to the collection of ceramic bricks that go inside them to store heat. So, some folks put them in the garage, while others fit them inside the house. The garage is obviously less ideal.
I can buy peak power at .0754 or off-peak at around .0450. It would be smart to buy all my electric heating BTUs at night but you have to buy the hardware, or maybe heat a slab during off-peak hours. Hydro utilities like to sell off-peak since the river never stops.
He didn't describe a unit sitting in a room. If that be the case, you would be somewhat right. But any loss to the room during a time you didn't want the heat would be considered an inefficiency (like having to use your furnace during the unoccupied period).
Not sure what you mean "True for energy, but not for heat. (There's a difference.)" Please explain what you mean.
I mean, there's a difference between heat and energy. Energy can do work. Heat -- maybe, maybe not. Once you've converted electric energy into, say, heat to heat a room from 55 to 70 (when it's 55 outside) the amount of "work" you can get out of that heat is miniscule -- basically proportional to 1 - ((55 + 460) / (70 + 460)), or about 3% of the energy originally in the electricity. So resistance heating is very inefficient in general, since all that "work" is essentially wasted (a heat pump is a far better deal). But there's no added inefficiency using a lightbulb vs an oil-filled space heater vs an old computer idling to convert the electricity to heat.
Agreed that if the unit overheats the room during peak periods there's reduced/no benefit, but a well-designed unit would shut down if this were going to happen.
Thanks for clarifying.
The storage unit WILL tend to overheat the room during the 'unoccupied' periods ... even if just a little ... which as I pointed out would be essentially an inefficiency. Hopefully it won't overheat the space during the peak periods ... assuming that is when you need the stored energy (which may or may not be the case).
In theory, if the unit is reasonably well insulated it shouldn't overheat the room. A thermostat should cut off the heater if the room temp significantly exceeds "set" temp (and cut off the fan when the room temp reaches "set" temp). Of course, it requires that the unit not be oversized.
You are not quite getting my point. Insulated or not, it will lose some heat (albeit a small amount) during the period when you don't want heat. I would be like forcing your furnace to run a little even when it is in the setback mode and above setback setpoint.
My point was, this loss will always be there and it will occur whether you need heat or not. Therefore it is less efficient than a conventional system that simple provides the energy when you want it.
It's like a water heater ... it loses heat to your house whether you need the heat or not (e.g. during the night setback or during the summer). That is an inefficiency of the system. It may be small, but when talking about energy use, it is still less efficient than a system that uses the energy when you need it, not before or after.
Again, the benefit of the TES is strictly in the shift of the energy use with respect to the rate schedule, not in its more efficient use of Btus. Run it side by side with e.g. an electric furnace (with e.g. essentially identical distribution) and it will use more energy.
Right -- there's no "efficiency gain" with heat storage, generally the opposite. But if we assume that the unit is being used during a period the year when heat is needed, to some extent, 24 hours a day, then the "escaping" heat isn't "lost" -- it merely supplants "immediate" heat that would otherwise have been required.
The "shoulder seasons" would be where things would be iffy -- often you get more than enough solar heating during parts of the day, and no additional heat is needed.
"it merely supplants
"it merely supplants "immediate" heat that would otherwise have been required." And that is part of my point. For the same reason we set our stats back at night, we wouldn't want heat to 'leak' into the room/house during periods we don't want it so it isn't 'otherwise required'.
Many if not most houses aren't designed for significant solar gain, so there is often not enough solar heating to do much of anything, so I tend to disagree w/ you about your second statement. It's pretty sad that houses aren't more solar oriented in this day and age. Builders and designers still ignore the simple principles of design orientation and you still see large developments that completely ignore the basic fundamentals of design orientation. Go figure.
Yes, their cost-effectiveness depends greatly on the off-peak rate break. If installed within the "conditioned envelope" so that there's no heat lost to the outside, either via conduction from the unit or from air leakage in the ductwork, then they should be nearly 100% efficient, but you still have to pay for their installation, and they still take up substantial square footage in the unit, so you probably need a rate break in the neighborhood of 50% for them to pay off.
ETS Heating system
The units that we are looking at are 10 1/2" deep, 24 1/2" high, and are from 30-58" wide, and weigh from 267-692#s; and are mounted via bracket 1 1/2" from the wall.
They contain high density ceramic bricks that act as the heat sink. They are charged/heated during the off-peak periods and then use that heat via a fan and thermostat and mocroproccessor controls to heat the rooms. I am sorry that the link didn't work for you, I was just on it yesterday. I hope that this additional info helps with this discussion. Again, thank you for your time and knowledge.
Kinda curious that they don't use water, which has the highest heat capacity per pound of any common material.
Yes.... ETS does really work. We love it...
The person you talked with really does know what he's talking about. These heaters are very efficient. The room units are located in the conditioned area of the home or condo. There are no energy or efficiency losses since all heat goes into area where you want and need it. The savings comes from using low-cost, offpeak electric rates which utilities offer. The heaters store energy as heat when rates are low and use this energy for heating all day long. So your savings will be the difference between your normal electric rate and the off-peak portion of the optional electric rate. Now there are various, standard electric heating systems being promoted that promise savings but contain now storage option. Be careful of these as they essentially are just a "space heater" which don't present savings. For storage heaters though, such as the ones you are referring to here and that we've had for quite some time, not only do these heaters provide very attractive savings on our heating bill, they are very comfortable, clean and reliable. I strongly recommend them.
What brand
do you have. Got a link?
peak power at .0754 or off-peak at around .0450
Did not realize your PUD had that big of differential. Over in the 'big county', PSE grabs us for 11cents 24/7. They had a nightime rate a few years ago and discontinued the break.
On the larger question of the 50% savings on storage, the off-peak rate would need to be 1/2 of the daytime rate for 50% savings, AND the thermal capacity of the 'heater' would need to be on the order of 50,000 BTU or more even for the small condos referenced.
Given a specific heat of ceramic of around 0.2, and that the ceramic gets heated to say 400F, the 'heater' would need to be about 800 pounds to supply heat thruout the day. Doubt they are that big.
BTW, did everyone know that if the Amish make a electric resistance heater, somehow a kW-hr magically generates about 8000 BTUs? <G>
BTW, did everyone know that if the Amish make a electric resistance heater, somehow a kW-hr magically generates about 8000 BTUs?
Actually, they only have to make the wood case for the heater to do that -- the heater itself can be Chinese. Them Amish are darn smart.
This should be an easy slam dunk. Just ask the electrician to produce his energy bills for the year prior and the year after he installed them in his house. That information is available from the electric company and would pretty much answer most of your questions. I'm betting he won't be able to produce them for one reason or another.
Yeah, the guy's obviously not going to be able to demonstrate 50% savings. 20% is probably the limit of what's possible, unless off-peak power is REALLY cheap.
50% savings are possible, but...
The savings are possible, I guess, but I am doubtful that we would realize such a significant difference. I did my own research so as to be able to get straight answers, better able to form an honest conclusion about this question. The difference for Time Of Use metering is 4.2 cents/kwh vs. 9.5 cents/kwh, if the utilities allow us to go there, vs. 9.3 cents/kwh that they are charging 24/7 now. But the kicker is that we would only be able to replace 2 or 3 of our 6 baseboard heaters due to space requirements and limitations. So I am guessing that the potential savings would net around 30-35% considering all other factors? Add in that we will need to purchase the Time Of Use meters and equipment(?) and the payback curve just got a lot longer.
Savings and Efficiency
Big K,
The efficiency of the units will be the same as the electric base board. There are inefficiencies in energy transfer but that shows up in the form of heat. As long as the ETS heaters are in the heated space and they aren’t over heating the space they are 100% efficient.
Unlike a water heater the ETS heater will not go to full temperature every day. Most use an outdoor sensor to decide how much stored heat is needed. Storage is determined by specific heat of the brick and temperature. The heaters will heat the bricks to nearly 1300 °F on the coldest days. That certainly meens that the insulation package must be very good.
The savings on the heating bill comes from the discounted rate that the power company gives. The percentage will vary depending on who the power company is. Generally it will be in the 40% to 60% range.
Al Takle, Steffes Corporation
"will heat the bricks to
"will heat the bricks to nearly 1300 °F" ... wow ... I guess you better have some serious insulation in that unit!! At that temp, I'm guessing you will have some serious inefficiencies going on!
With adequate insulation the max temp should make no difference in "efficiency". The max temp is simply a tradeoff between insulation thickness and heater element robustness on the one hand and the weight/size of the "thermal mass" on the other. Higher temp permits more stored heat for a given thermal mass.
yeah, well it's one thing to store heat up to say around 100-200 degF max ... entirely a different thing at 1,300 degF. Insulation has to be different, heat loss goes through the ceiling ... and the 'efficiency' will likely drop way off. I've a feeling the heat loss from such a stored temp would be relatively huge unless you spent a small fortune on some special insulation!!
I agree that you have to spend more on insulation, but there's no conceptual difference. You just need more insulation at the higher temp to achieve the same heat loss.
Yeah, except that we are moving past concept to something much more with this. I don't think you are reading this and really thinking about it. Frankly I thought the statement was a typo, which is why I commented. Storing energy at 1,300 degF is decidedly a much different animal than "just" needing more insulation. Maybe I missed something along the conversation here; but containing (what I assume to be) a significantly large mass (as large as a desk??) at 1,300 degF is no small task.
Yes, "conceptually" "just" insulate and you are good to go. Those are the two words that are easy to say, but difficult to achieve in this application.
So you're saying that what they did is impossible?
Brick Temperature
The higher temperatures along with the dense brick give the ceramic brick heaters have about a 10 to 1 volumetric advantage over water.
The insulation package must be up to the task. That said most people like warm cabinet for comfort reasons.
First of all, I'm not certain what "they" did. Second, based on the smattering of information that describes this system, I have a sense that maybe someone made an error in a statement (who has so far not confirmed one way or the other) about the storage temperature of this device or simply has omitted some other detail of this storage (e.g. the volume).
Thermal storage temps in the range of 100-200 degF would be/is common for both water/liquids and solids. Insulating such a container is fairly straight forward and doesn't require it to be excessive and can use some readily common materials available from the lumber yard.
Thermally insulating a storage temperature of over 1,000 degF, particularly if large could be a very unusual task. Not even high pressure/temp steam systems operate up in that range. There are clearly insulating materials that would work ... but I suspect they aren't common building materials ... even for commercial construction.
I could have easily missed something with the system being described. Precluding that, I stand behind my tendency to be skeptical about insulating what I assume to be a fairly large thermal mass at 1,300 degF.
Would you say that ceramic brick is a pretty good insulator?
Our electric oven, with a wall thickness of about 2.5", can go up to 550F.
No, I don't think I would consider it a good insulator. My guess is that ceramic brick has a fairly low R-value.
Doesn't mean it can't protect you from a high temp ... much like the skin of e.g. the shuttle. I've seen lots of products that claim to be good insulators 'just like the material on the shuttle'. But that's a different animal.
Your electric oven doesn't maintain that temp for 12+ hours. Now increase that temp by 2.5 times and try to store that heat for many hours. You need some serious R-value.
Going back to my original point ... at that temp, it seems the inefficiency of heat storage must be very large (i.e. the heat loss of the storage device).
Again, also, I know very little about the specifics of this product/system, so maybe there is something about it that is contrary to the concept I have about temperature, volume of storage, etc.