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  • This is why an ETS system works for me

    Most of the regulars on this site know that I am a fan of ETS (electric thermal storage) systems.

    Here is a graph of why I like the capabilities of these systems:

    Solar ETS Graph.jpg

    Single digits again tonight, but warm and cozy inside.

  • #2
    Originally posted by DanS26 View Post
    Most of the regulars on this site know that I am a fan of ETS (electric thermal storage) systems.
    Single digits again tonight, but warm and cozy inside.
    If those systems could work efficiently over a year instead of a day, I wouldn't need a grid tie so desperately. But
    I suppose it would be as big as the house. They used to keep river ice available all year in big sawdust pits.

    Contained within the house, I suppose your storage efficiency is 100%? Bruce Roe

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    • #3
      Originally posted by bcroe View Post



      Contained within the house, I suppose your storage efficiency is 100%? Bruce Roe
      Well not quite....but better than a well insulated water heater but worse than a YETI cooler.

      Comment


      • #4
        Thermal storage systems as a way to heat dwellings have been around almost as long as there's been shelter.

        One of the keys to a successful thermal storage system, besides the thermal mass itself, lies in the overall gross building loss coefficient, including infiltration loss (or gain) and reducing that loss as much as practical. The other is a high as possible ratio of the building thermal mass to the overall loss coefficient.

        Dividing the "effective" thermal mass, M*cp = "effective" mass * specific heat (in BTU/deg. F.) by the overall gross building loss coefficient, U*A (in BTU/(hr.*deg.F.) gives a result who's units are hours. That's called the building time constant.

        Thermal storage systems, regardless of the heat source - PV, grid electric, nat. gas, solar thermal, etc., work by increasing the effective building time constant. That will include allowing time shifting of loads. It ain't rocket science. Been around about as long as the concept to the exponential function or longer.

        Most modern single family residences might have time constants of 15-30 hrs. or so, maybe more for highly insulated and sealed buildings, with temperature decay following the same route as voltage decay in an electrical circuit with the thermal mass being analogous to capacitance.

        Knocking the heat loss in half has the same effect on the time constant as doubling the effective thermal mass. The temp. of the interior of the building will change more slowly with a longer time constant.

        Assuming steady state conditions, when the time without energy input to the building == (M*cp)/(UA), or one time constant, either heating or cooling, the inside to outside temperature difference will be equal to .368 of the initial inside/outside temperature difference. That's a hard value to verify for most residential situations.

        So, buildings with low heat loss coefficients need less thermal mass for the same effective time constant. I verified this in an existing home I owned in Buffalo many years ago. Built in 1928, I measured the home's original building constant to be ~ 7- 8 hrs. After about 2 yrs. of mods. - sealing, insulation window treatments, etc., I knocked the heat loss down to about 1/3 of the initial value and the time constant went up to about 20-22 hrs. or so. I calc'd the effective thermal mass of the house from timing the forced air furnace runs and getting estimated furnace efficiency from temps. and flue gas analysis from cold starts to heat a steady, asymptotic building interior temp. I also wanted to distribute a couple thousand lbm of bricks and water jugs near the furnace outlets to gauge the effect of increasing the thermal mass, but SHMBO, (who could otherwise give Job lessons in patience) had reached her limit, so, I took what the textbooks told me about that aspect of thermal capacitance on faith.

        It may be easier to add thermal lumped mass systems to a dwelling, but if there is not a good way to get a lot of heat into and out of the lumped system quickly as indicated by the ratio of what is the "effective" thermal mass to the gross thermal mass (that is, the ratio of what's usable or "cycleable" to the (gross mass* blended cp), and not unlike something known as the "Biot" number for those interested), the results may be less than optimal or expected. Sometimes, sealing the building envelope and adding insulation is less troublesome, less expensive and easier than adding enough thermal mass to accomplish the same thing, which again, is, bottom line, all about increasing the building thermal time constant and little else - other things, like time shifting of loads comes along for free.

        As for charging the thermal mass or thermal "capacitor", if I was going to do it with solar energy, I'd probably first look at solar thermal, and air cooled collectors rather than PV. Air cooed collectors are about the simplest type of solar collector known (after a widow, or a black cat laying next to the sunny side of building in winter), a lot simpler to build (read <<$$) and maintain. Leaks and freezing are not a consideration as for water cooled collectors. They'll probably take up less space for the collectors than PV because they will probably collect about 2X as much energy for the same area as PV. The store will need a different internal distribution system as the air will be a lot cooler than resistance a heater. However, that's a very well developed science and manageable.

        In a very real sense, most of the cost savings from not using PV (and then turning the electricity thus produced into heat) will be will be due to entropy: Making electricity causes a much larger entropy increase than simply heating from the sun directly, and that entropy increase comes at a cost. The thermal losses are a bit higher than with PV, but the greater overall efficiency, likely 25-30 % or a bit more vs, 15-18 % for PV or less, along with the cost savings more than and easily makes up for it.

        For what I think I may know, electric thermal storage is a tough sell.

        Take what you want of the above. Scrap the rest.
        Last edited by J.P.M.; 01-08-2017, 01:36 AM.

        Comment


        • #5
          Heat away. I turn excess solar into hot water. Batter than batteries or selling it back to a utility. To me it is all about the control system. Either the control systems are too stupid, too expensive, or set up wrong. If I didn't design my own controls it wouldn't be cost effective. It takes time for the world to catch up. Very early 70's the IEEE award for best new microprocessor use went to a microprocessor based toilet (what you see today). That only took 40 years to come into common use.

          Comment


          • #6
            Originally posted by PNPmacnab View Post
            Heat away. I turn excess solar into hot water. Batter than batteries or selling it back to a utility. To me it is all about the control system. Either the control systems are too stupid, too expensive, or set up wrong. If I didn't design my own controls it wouldn't be cost effective. It takes time for the world to catch up. Very early 70's the IEEE award for best new microprocessor use went to a microprocessor based toilet (what you see today). That only took 40 years to come into common use.
            Yes, you hit the nail on the head, it is all about control to make these ETS units work and be cost effective. The room sized units I use have both an outside thermostat and an internal room thermostat to control the charging level. So the charging level is variable based on outside temps and the required heat output for the room. Hands off operation which I like.

            Built in timers allow me to only charge when the sun is up and only charge one unit at a time. That allows me to keep the power usage under the solar production range. On top of that I can control for room temp setback to increase efficiency. All of this is programmable.

            Speaking of microprocessor based toilets......after a trip to Japan where they are ubiquitous.....I decided to install a unit in each of my bathrooms. Finished the job this week. Don't know why these have not caught on here in the states.

            Comment


            • #7
              Originally posted by DanS26 View Post

              Yes, you hit the nail on the head, it is all about control to make these ETS units work and be cost effective. The room sized units I use have both an outside thermostat and an internal room thermostat to control the charging level. So the charging level is variable based on outside temps and the required heat output for the room. Hands off operation which I like.

              Built in timers allow me to only charge when the sun is up and only charge one unit at a time. That allows me to keep the power usage under the solar production range. On top of that I can control for room temp setback to increase efficiency. All of this is programmable.

              Speaking of microprocessor based toilets......after a trip to Japan where they are ubiquitous.....I decided to install a unit in each of my bathrooms. Finished the job this week. Don't know why these have not caught on here in the states.
              What can I microprocessor based commode do that I can't do by using the handle ? I seem to remember a joke or 2 from my youth about automatic toilets that perform various functions and how things can go wrong.

              Comment


              • #8
                Originally posted by J.P.M. View Post

                What can I microprocessor based commode do that I can't do by using the handle ? I seem to remember a joke or 2 from my youth about automatic toilets that perform various functions and how things can go wrong.
                Just review the TOTO product line....toilets have come a long way. And yes they work superbly.

                Comment


                • #9
                  The problem is in commercial buildings the handle thing is left to the next person. Also the toilet needs to be flushed every so many hours whether it is used or not.

                  Comment


                  • #10
                    Originally posted by DanS26 View Post

                    Just review the TOTO product line....toilets have come a long way. And yes they work superbly.
                    Will do. Thanx for the tip.

                    Back to toilet flushing school for me.

                    Comment


                    • #11
                      Originally posted by J.P.M. View Post
                      Thermal storage systems, regardless of the heat source - PV, grid electric, nat. gas, solar thermal, etc., work by increasing the effective building time constant. That will include allowing time shifting of loads. It ain't rocket science. Been around about as long as the concept to the exponential function or longer.

                      Knocking the heat loss in half has the same effect on the time constant as doubling the effective thermal mass. The temp. of the interior of the building will change more slowly with a longer time constant.

                      For what I think I may know, electric thermal storage is a tough sell.
                      Almost intuitively obvious, isn't it? I saw the time constant change when the hot water circulator system (with
                      home brew control) was fully insulated. Also discovered that common pipe insulation might keep pipes from
                      sweating, but in fact performed very poorly as insulation. Haven't developed an improved insulation scheme yet.

                      One thing I never hear mentioned, is that the better a house is insulated (increasing the thermal time constant),
                      the less benefit there is from an automatic timer setback thermostat.

                      However my problem is getting good storage efficiency over 12 months, which directly drives my use of PV solar
                      collection/grid tie. Collection efficiency is low, but convenient, low maintenance, with 100% storage efficiency!

                      As for a microprocessor based commode, the theme here is the most simple and rugged system will fail least and
                      be easiest to fix. With all the plumbing repairs that come up, here there will be no micros involved. As it is, a lot of
                      extra shutoffs and unions are added to make it easier to isolate an area without whole house shutdown. Bruce Roe

                      Comment


                      • #12
                        Originally posted by bcroe View Post

                        Almost intuitively obvious, isn't it? I saw the time constant change when the hot water circulator system (with
                        home brew control) was fully insulated. Also discovered that common pipe insulation might keep pipes from
                        sweating, but in fact performed very poorly as insulation. Haven't developed an improved insulation scheme yet.

                        One thing I never hear mentioned, is that the better a house is insulated (increasing the thermal time constant),
                        the less benefit there is from an automatic timer setback thermostat.

                        However my problem is getting good storage efficiency over 12 months, which directly drives my use of PV solar
                        collection/grid tie. Collection efficiency is low, but convenient, low maintenance, with 100% storage efficiency!

                        As for a microprocessor based commode, the theme here is the most simple and rugged system will fail least and
                        be easiest to fix. With all the plumbing repairs that come up, here there will be no micros involved. As it is, a lot of
                        extra shutoffs and unions are added to make it easier to isolate an area without whole house shutdown. Bruce Roe
                        You would think so, wouldn't you ? Unfortunately or otherwise, my experience in dealing with folks in such matters such matters is that common sense sometimes isn't so common.

                        On pipe insulation: In general, pipe insulation will seem less efficient than expected for several reasons. For 1 thing, pipe insulation is often relatively thin (~ 1/2") w/R values of about 2 or so, and often poorly applied. The air over bare pipe will have an R value of about one. Also, and of a bigger influence most of the time, is the fact that the ratio of surface area to contained volume of a pipe is, depending on length and dia. of pipe involved, something like 6 or 7 times larger than that of a right circular cylinder with the dia. equal to the height., meaning a lot more surface area to lose (or gain) heat through. Example: 100 ft. of 1" dia. tubing has the same approx. volume as a 10 5/8" dia. cylinder, 10 5/8" high ~ = 942 in.^3., but a surface area about 7 times as great ( ~ 3,770 in.^2 vs. ~ 532 in.^2) from which to transfer heat ~ 7 times faster to or from the contents. Partial solution: Get fatter pipe and 1" Armaflex insulation. Before that, if you're interested in hot (enough) water without too much $$cost, turn down the temp. settings, and/or get mixing valves at the tank, scrap any recirculation, get low flow faucets/heads and 1500 W spot heaters for boost at points of use.

                        True about set back thermostats, the higher the time constant, the less the interior temp. will change as f(time), but better insulation, and usually equally or more important in terms of economic return, better sealing, will always result in lower heat transfer with lower bills to show for it. The lower the building time constant, the more the bills will be lowered by a set back thermostat, those savings being governed by the RATE of change of temp. (2d derivative) as well the inside/outside temp. diff., but that's a bit of false economics - you might save 20% of a $200 HVAC bill with a set back thermostat and poor insulation, but only 5 % of a $100 HVAC bill in a well insulated building. I don't know if I'd insulate the building and then compare the cost of the setback thermostat against the 5 % savings, or do the setback thermostat before insulating because the payback on the thermostat is probably quicker and it costs less, and then insulate until the cost equaled the life cycle savings over however long a time period I chose. I'd probably do both, with the setback thermostat first.

                        For that matter, high insulation levels mean less savings per degree of setback, but no one is saying lowering thermostats in the winter or raising them in the summer is still not a good idea. That cost (changing thermostat settings) is still zero with an immediate payback - just that more insulation is less cost effective as a result of lower (higher) thermostat settings.

                        Effectively using or considering the grid as a storage medium via net metering is certainly one of the considerations and ways to look at net metering. But in doing so, the costs may need to take some account of the way seasonal storage system costs are accounted for. I'm not quite sure how the accounting would work for that, especially when assigning a value to the convenience and maintenance, but I'm quite sure it's possible.

                        Still, and one aspect I'm pretty sure of, is that using electricity to supply most or all of the heat to a residence via resistance heating elements when other means of heating are available is almost always more costly whether or not thermal storage is involved. In such cases, with the possible exception of some spot temp. boosting, using electricity to heat things is still like cutting butter with a chain saw. Use fossil fuels. To those who say it's better to use the excess PV electricity than the paultry sum the POCOs pay for excess generation, I'd respectfully suggest better sizing methods during design, and less oversizing up front is a lot better in the cost effectiveness dept.

                        I'm with you on KISS for commodes. Life is complicated enough. Somehow, high tech crappers seem like an invasion of my privacy, but opinions vary.

                        Comment


                        • #13
                          "I'd respectfully suggest better sizing methods during design,"

                          Got a formula? Or is this like pornography, "I know it when I see it"?

                          Comment


                          • #14
                            I have four sources of heat in my house.....wood, propane, grid electricity and PV power. I can pick and choose which heat source I want to use. To make my choice I weigh in a variety of factors.....cost, convenience, efficiency and comfort.

                            Wood at $65 per rick delivered is least costly at ~$5.20 per MMBtu is comfortable but it is very inconvenient and messy.

                            Propane at $0.879 per gallon (yes that is actual price I paid for summer fill up) is ~$10.43 per MMBtu is comfortable, convenient and, at least for now, somewhat affordable.

                            Grid electricity at $0.105 per kWh is ~$30.76 per MMBtu is comfortable and convenient but is very expensive to use as heat.

                            PV power at $0.03 per kWh (yes that is my actual production cost) is ~$8.82 per MMBtu is comfortable but somewhat inconvenient since I only heat two rooms with it through my ETS systems. But in those two rooms it is very efficient and cost effective.

                            So there you go....I use my ETS systems and supplement with propane for heat because at my age I like comfort and convenience. Its not rocket science.
                            Last edited by DanS26; 01-09-2017, 12:47 PM.

                            Comment


                            • #15
                              All true. The handyman store pipe insulation is warm to the touch, and I don't have any on
                              the 5/16" return line. I note the foam I put on garage doors doesn't feel cold to the touch at
                              all; maybe some of this could be grooved to fit over both the main pipe and the circulation
                              return line together? The length is nearly equal to the length of this noodle shaped ranch;
                              don't think increasing diameter is to my advantage. The day the circulator pump stopped,
                              I heard about it immediately. The temp is set low enough that a minimum of cold water
                              mixing is needed. Restricted shower heads are for people who waste too much time in
                              the shower, instead of getting on to other matters. Seems pretty silly when there might
                              be a pool on the property.

                              Most months temp control here is achieved by a fairly efficient heat pump; relatively
                              few days rely entirely on resistance heat. Of course a clean sheet approach suggests
                              insulate to the max; use a very efficient heating and cooling plant, and build the minimum
                              size solar plant. In reality the heat pump is relatively competitive with propane here, and
                              I have seen times when even resistance heat was only half the (manipulated) cost of
                              propane. And the smaller class PV system rules weren't the ones I wanted to be under.

                              Time wise, it doesn't take long to throw up a very capable PV solar system. It takes
                              longer to get a really good set of state-of-the-art heat pumps in place, and the full
                              insulation upgrade can run into many years and in some cases pretty big bucks. While
                              annual energy collection has been pretty consistent here, usage has varied hugely with
                              the weather; so much for "just right sizing".

                              Each will chose their own priorities, I have mine. Creature comforts will come first
                              without compromise. The idea of of supplying all home energy without burning any
                              kind of fuel on or off premises appeals to me. And minimize the number of utilities
                              I must connect to, each adds their overhead cost (recently observed to be growing
                              exponentially). The circulator will continue to run.

                              The PV system cost isn't a problem, and is giving lots better ROI than so many of
                              the things I see being bought everywhere. I own a lot of chain saws. Bruce Roe

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