This is why an ETS system works for me

[bcroe]

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

[J.P.M.]

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.

[PNPmacnab]

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.

[DanS26]

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.

[J.P.M.]

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.

[DanS26]

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.

[PNPmacnab]

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.

[J.P.M.]

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.

[DanS26]

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.

[bcroe]

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

[DanS26]

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.