Heat Modeling (not Kate Moss)

gasfolk

Hi Rich W,

Recent data suggests that high Moss leads to low Moss and then slow recovery of the model, perhaps heralding a change in climate. Could affect your modeling career. I think we can all agree on that. : )

Any luck with a first stab at a circuit? Any idea how to calibrate the thing? Any resources you need? Anything else we could do or discuss to be helpful?

A while ago you asked what my ultimae goal is for this model. I would like to find either a cache of data or a simple tool to explain why the thoughtful people above have (slightly) different opinions on high mass. They are all smart (been readng their posts for a year) and probably all correct depending on starting assumptions, and it would be neat to be able to tweak those starting assumptions. BTW, I am not in the industry and have no axe to grind and no stake in any particular answer or outcome. Just curious.

Could you make this a useful tool?

Best regards,

gf

gasfolk

RL Circuits?

Looking for criticism or comments on design of a (strictly amateur) simplified "DC-circuit" model of heat flow through a structure. Would welcome any advice on the following assumptions:

1. A boiler can be viewed as a DC power source?

2. Walls as a resistor and inductor in series?

3. Outdoor "weather" as a variable DC power source?

4. Internal thermal mass as an inductor?

Hoping to identify useful parameters that could be measured (like the Eatherton or Boilerpro Real Time Loads or perhaps a real-time estimate of thermal decay) to allow better categorization/differentiation of various structures.

Thanks for any thoughtful comments,

gf

gasfolk

RL Circuits?

Looking for criticism or comments on design of a (strictly amateur) simplified "DC-circuit" model of heat flow through a structure. Would welcome any advice in general or specifics about the following assumptions:

1. A boiler can be viewed as a DC power source?

2. Walls as a resistor and inductor in series?

3. Outdoor "weather" as a variable DC power source?

4. Internal thermal mass as an inductor?

Hoping to identify useful parameters that could be measured (like the Eatherton or Boilerpro Real Time Loads or perhaps a real-time estimate of thermal decay) to allow better categorization/differentiation of various structures.

Thanks for any thoughtful comments,

gf

jp_2

inductors?

I would think you'd do better using capacitors for internal loads, your varying dc weather will be at a real low Hz therefore inductance has little affect.?.?

hard part is making an accuarate circuit of a structure and the associated variables.

best bet is to come up with an overall R value and heat capacity for a structure.

Mike T., Swampeast MO

1) The boiler is only "straight" DC if it cannot modulate--otherwise it's a variable DC power source?

2) Offhand sounds decent but quantifying how much it's acting as an inductor for a given level of resistance is, let's say, difficult...

3) Outdoors is AC!!!!!!!!

4) When 1) works through 2) to balance 3), 4) ceases to have meaning.

Brad White_89

Ooooh.

Mike, that was worth an "ooooh".

Eloquent.

gasfolk

Inductors vs Capacitors?

Hi JP,

My thinking was that as a wall fills with heat it becomes easier for the heat to flow through, and if a boiler is a DC source, then an inductor would have that property? As they charge capcitors resist current flow?
Although variable, the boiler output seems to flow in one direction, so DC??

gf

gasfolk

AC circuit...

Hi Mike,

Good point--it IS an AC circuit with a variable DC source (boiler). In hope of simplified DC analysis, would restriction to part of the year allow simplified, DC weather. If so, over what period (heating season, winter, January, ??) might that assumption be valid or invalid??

gf

gasfolk

The follow-up question is...

what period is most intersting to model? Midwinter because of peak loads? Shoulder seasons because more fuel is burned during these times? End of season because of complicated switching (heat to A/C) issues?? Other thoughts?

gf

Constantin

Sure you can...

... control system theory / state-space doesn't care if you're modeling electrical, kinetic, thermal, etc. systems, the analogies are the same, even if the unit measurements differ.

On the other hand, modeling a home correctly using all the elements of design control theory (i.e. the flywheel effect, thermal short-circuiting, multiple insulation values, etc.) would quickly become a rather convoluted FEA excercise. I'm not convinced it's worth the effort, but that's just me.

On the other hand, Siggy would do very well to integrate/adapt SPICE into his hydronic design program. It would allow heating contractors to model ahead of time what each circuit would be doing as the pumps, zone valves, etc. modulate. That could be a very powerful trouble-shooting feature. The only problem is determining all the analogous values, such as Cv for items that do not always get their Cv listed (i.e. boilers).

jp_2

C or L

good question, I would guess the V=temp and I=btu's.

so maybe its an RCL circuit? i would think that V always leads I here.(temp 'ahead' of btu output)

as I see it though, you were saying as the wall "fills" with heat... I see this happening when the inside and outside temps are becoming equal, so heat flow slows. if heat flows easier at higher temps, your R value would become a function of delta T.

i agree with the variable DC boiler.

jp_2

#2

"""""2) Offhand sounds decent but quantifying how much it's acting as an inductor for a given level of resistance is, let's say, difficult..."""""

I'd say not difficult at all, resistance is R value(or U)
and the dampening value(either C or L) is the heat capacity of the wall(thermal mass, not just mass).

gasfolk

V leads I...

I agree.

1) A structure at 0*F, everything at steady state.

2) Switch on the heat plant.

3) Initially all heat (except stack losses) is retained in warming the house.

4) At some point enough Btus have migrated into the shell that some reach the outside and begin drifting away (but with no substantial affect on the environment, so outside temp remains steady at 0F).

5) The wall progressively warms till steady state between heat added by boiler and heat lost to environment (based on delta T from shell to environment??) and--at this point the wall is "full" and each Btu added on the inner surface simply balances another lost off the outer surface).

Would a capacitor in parallel with a resistor satisfy? Would internal (completely isolated from the shell) thermal mass be better modeled with a capacitor??

gf

gasfolk

\"Integrate/adapt SPICE\" = Kate Moss?

Hi Constantin,

My goal is not a detailed model with hundreds of resistors and capacitors--though I do see the value in that approach.

My interest is to better understand useful parameters by simplifying. First with a concept circuit, then looking for simple approaches to measure and explore those parameters. One benefit might be better categorization of structures For example, my house may be low heat loss, high thermal mass, and it would be nice to have numbers for that.

Eatherton and Boilerpro outlined approaches to measure steady-state heat loss (at whatever steady outside temp). Perhaps there is a simple way to quantify thermal mass.

A simple circuit model may suggest other things to differentiate one house from another. Early car enthusiasts found a variety of performance characteristics worth measuring. There is real value in Manual J, but I've learned something from measuring the "real time" heat loss.

Sorry this is a little repetitve and disjointed. I'm being pulled away...

Best regards,

gf

gasfolk

Perhaps a fool's errand, but...

If you could be absolutely sure of the peak, design-day heat loss, might you recommend a different boiler/furnace in a high versus low-mass house? Might a low-mass house require higher heat output to cover even brief, seasonal hours when it's below design temp? The opposite for a high-mass house?

With constantly changing outdoor temp, solar heat gain, wind, occupancy, etc., a house is rarely at steady state, so could thermal mass be relevant? Other real time measures?

Constantin, what is SPICE? Reference or link?

Thanks,

gf

Rich W

Variable inductor in an AC circuit might work.I like the capacitor idea with a bleed resistor as heat loss. A second resistor(PTC thermister) in parallel with the first would simulate colder outdoor temps and faster heat transfer throught the wall (lower ohms= faster discharge of the capacitor=lower heat in the house). Operational amplifier monitoring the voltage of the cap. would ramp up trying to keep the voltage of the cap. constant. Or you could make it like a bang-bang control: Set-up the amp to turn on at say 11volts and run until the cap. reaches 12volts.This of course charges the cap. through a third resistor (piping/radiation). Cool idea gasfolk. Is this for a demo for a homeshow?

Christian Egli_2

No, not a banana split

What a nice memory you brought back from the past. In a new age of computerized simulations where everyone is glued to a picture screen, your electric model made me remember the "computers" once used in the lab.

You'll recall the playthings that looked like a the peg boards at the telephone exchange. You had lots of banana plugs and cables. You also had the choice of resistors, capacitors and inductors. Lastly, when connecting the dial potentiometer you were ready to wake Frankenstein. I also remember the big, live felt pen operated, x-y plotter. Paper jams and heaps of fun.

We could precisely simulate and compute the response of thermal systems. Nothing new has happened since. Of course, all this can be done on a computer with Labview and Matlab and others. Dial in whatever you want from the input generator (and for Midwest climate, select random...) and observe the output.

What equipment have you got?

I'm not sure exactly what an inductance represents in a thermal system, I would mostly be concerned about the two others, though I'm curious now.

As long as you are happy considering your home as one uniform mass in relation to the environment, I see no need to do finite element modeling. This would be fascinating if you wanted to predict temperature distribution throughout your space -but I didn't get the sense that that's what you wanted to do.

You want to study boiler (so called) oversize in relation to indoor temperature stability. The trick being, to find what the smallest boiler can possibly be, without falling into the ineffective category of trying to heat your home with just a cigarette lighter. For that, I would study the frequency response and the amplitude ratio.

Back to kids games, remember playing tag at recess, and you're it and you're running after the other kids and neither your game strategy nor your leg power is adequate to just blast yourself to the next phase of the game? so instead you find yourself running towards kid no. 1 without even getting near, now you see kid no. 2, you run after that one without getting near, then you try chasing no. 3, and so on. That's an amplitude ratio problem, lots of effort, wasted results.

To get the worse whack out of your temperature response, I would study the worst part of the winter, which isn't the coldest. It's the parts where you experience the greatest weather change in the shortest laps of time. Again, for my Midwest climate, this would be an input amplitude of about 60 degrees F over a one afternoon frequency. Then, fiddle with boiler size to see how well your response follows. The small boiler is not the one that responds with the least wasted heat -there is no point in adding heat on top of an already cresting heat wave, you want the boiler sized so it can precisely fill only the temperature dips without spilling over.

Playing with the resistance will show there is an upper limit to what is good as far as insulation, and playing with the capacitance will show all the perverse effects of the thermal mass eluding so many in the pursuit of the passive house.

What should be fascinating is to incorporate wet bulb temperatures into the game and then see whether there is a difference between standard air conditioning, high velocity or mini split. (This still bugs me a lot)

Meanwhile, in your simulations, I am rooting for steam to show up as a solid winner. Observed as a whole house system it probably is. But as an aside, I do think people who understand one pipe steam sizing issues have all these complex heat loss / boiler load already intuitively under their belt.

If I were running a hydronics school, I would study one pipe steam a lot. It opens lots of doors. It's the equivalent of studying Latin in order to better understand the workings of English.

Oink oink.

S Ebels

Thinking out loud

"If you could be absolutely sure of the peak, design-day heat loss, might you recommend a different boiler/furnace in a high versus low-mass house?"

I might recommend a different peak output but not a different type of boiler. A modulating/condensing appliance solves a world of problems, especially when coupled with proportionaly controlled heat emitters. You can size for worst case plus a little and the boiler will compensate when conditions don't demand full output.

"Might a low-mass house require higher heat output to cover even brief, seasonal hours when it's below design temp? The opposite for a high-mass house?"

Well let's see here..... In your first question, you said "peak design day" and in the second one you refered to "below design temp". I think the thermal mass would have to be very low indeed to warrant the installation of a greater than "normal" output. I've tried to experimentand model those conditions using different R-values and structure types on my normal heat loss program. (HVAC-Calc) Once you have the basic sq ft established along with windows, doors and ceiling heights, playing with the framing and/or r-values usually turns up a less than expected difference, at least in my experience.

While we all know that brief interludes of below design temp occur with some regularity, I feel that current methods of heat loss calculation have enough "fudge factor" built in to accomodate those periods. Perhaps that's what you're driving at..........an absolute "gold standard" heat loss that is accurate down to the last BTU? That would seem to be a worthy goal but given that people change their houses from time to time structure-wise and the sheer magnitude of the variables encountered with weather conditions alone, why would you want to size something that close?

"With constantly changing outdoor temp, solar heat gain, wind, occupancy, etc., a house is rarely at steady state, so could thermal mass be relevant?"

I agree that no such thing as steady state exists in the real world. That being said, I have observed that high mass buildings do a lot to smooth out those thermal bumps and dips in the road. A couple jobs in particular come to mind. One is a log home we did a couple years ago that utilized 14-16" whole logs. The owner has stated repeatedly that he notices no change in operation of the boiler when overnight temps drop as much as 30-40* from daytime highs. He has said that the temp has to go down and stay down for several days before he sees an increased firing rate or cycling of the boiler. The other is a concrete structure that is has a berm on three sides. The owner of that place notices the increase in mass at the tail end of each season. Each season being heating and cooling. His A/C system doesn't come on until July regardless of it being 90* earlier in the summer season. The same holds true with the heating side of the coin. His system runs very little in the early part of the winter even if the temps drop to well below "normal" for a day or so. He says it's late January to early February before the heating plant runs much at all. This would seem to indicate that high mass does "soak up" some of the afore mentioned "bumps in the road". By the same logic though, once his house and the ground around it are cooled to late winter conditions the system has reached its steady state conditions and from there on behaves much like any other house. I think he probably spends a little more on fuel during the late spring because of the reverse effect when coming out of a winter weather period. IE: winter into spring. Then the mass is working against him.


I'm purposely ignoring your first set of questions because you are way over my head when it comes to the electrical analogy. I choose to remain silent on those issues and be thought a fool rather than to open my mouth and remove everyone's doubt.

Great topic and I'm looking forward to the ongoing discussion.

Constantin

Hi!

Sorry for the late reply...

Your points are well-taken. Could one dictate different boilers on the basis of mass? Sure, but the question is one of degrees, no? I mean, a earthship will probably require a boiler with less "peaky" output because it's mass smooths out anything that goes on outside. Similarly, a single-wall tent will require a lot more modulation to stay comfortable...

So where does that leave you? I would say that investing in a WEL or a similar device that monitors the responsiveness of your extant system to changing exterior conditions may give you the empirical insights you are seeking.

As for SPICE (Simulation Program with Integrated Circuit Emphasis), please excuse my not explaining it further. SPICE or pSPICE is a electronic circuit analysis program that allows users to design complex circuits and see how they respond in ways that traditional analysis allows, but which would be VERY time consuming to calculate by hand. Amazon has one reference I could see right away. Presumably, there are others.

In Siggy's context, using SPICE would allow the user to simulate the flow of water through the whole system and see how it responds to varying conditions. It could be of particular value to people who are sent in to do forensic repairs to hacked systems.

gasfolk

SHell vs. Thermal Mass

Perhaps thermal mass in the shell is negligible compared to the internal thermal mass? If so, perhaps reasonable to simplify to a resistor for the shell and a capacitor for the thermal mass?

Does it seem reasonable that thermal mass in the shell could behave so differently from that in the core to warrant special treatment?

gf

gasfolk

Nice...

Hi Rich W,

Good suggestions. No demonstration planned (as I am a strict amateur). Could you do one? Would any discussion here help with design and presentation?

gf

gasfolk

Good thinking...

Hi Steve,

"You can size for worst case"--
As Brad White and others have written, if Manual J assumes worst case heat loss through all surfaces--simultaneous wind from all directions, N,S,E,W--(which is absolutely necessary for sizing radiation and ducts), summing those worst-case room loads may contribute an unintended "safety factor" in boiler sizing. That's ok if it's recognized, but perhaps we should call MJ results the Kansas (or "Ozian") heat loss to distinguish from a measured or "real time" heat loss.

"An absolute "gold standard" heat loss"--
If the Ozian heat loss protects homeowners from thoughtless installers, perhaps the thoughtful contractor might use the Eatherton/Boilerpro heat loss (and perhaps a real time estimate of thermal mass) and do some fine tailoring? Eatherton and Boilerpro seem to size to these measured loads without a problem.

"High mass buildings do a lot to smooth out those thermal bumps and dips"--
If we could measure and quantify this, perhaps we could calculate minimum mass to retrofit to have a beneficial effect. If European houses are massive compared to American houses, perhaps we can better measure those affects.

Just a quick note--still pondering your comments. I took my EE courses nearly 30 years ago--dim (and dimming) memories, and I understand quite out-dated. Ouch!

Best regards

gf

gasfolk

Good thinking...

Hi Steve,

"You can size for worst case"--

As Brad White and others have written, if Manual J assumes worst case heat loss through all surfaces--simultaneous wind from all directions, N,S,E,W--(which is absolutely necessary for sizing radiation and ducts), summing those worst-case room loads may contribute an unintended "safety factor" in boiler sizing. That's ok if it's recognized, but perhaps we should call MJ results the Kansas (or "Ozian") heat loss to distinguish from a measured or "real time" heat loss.

"An absolute "gold standard" heat loss"--

If the Ozian heat loss protects homeowners from thoughtless installers, perhaps the thoughtful contractor might use the Eatherton/Boilerpro heat loss (and perhaps a real time estimate of thermal mass) and do some fine tailoring? Eatherton and Boilerpro seem to size to these measured loads without a problem.

"High mass buildings do a lot to smooth out those thermal bumps and dips"--

If we could measure and quantify this, perhaps we could calculate minimum mass to retrofit to have a beneficial effect. If European houses are massive compared to American houses, perhaps we can better measure those affects.

Just a quick note and still pondering your comments. I took my EE courses nearly 30 years ago--dim (and dimming) memories, and I understand quite out-dated. Ouch!

Best regards

gf

gasfolk

Insight...

You may be right. The WEL will certainly give a lot of interesting data, and perhaps the gdanken experiment of DC-circuit modeling of heat flow may also be useful as a lens to focus our view and interpretion of that real time data. Perhaps this has been done before, but I can't find references.

Thanks for the SPICE reference (which I am pursuing) and for your good thoughts.

gf

jp_2

good question.

thermal mass could occupy its own thread. my guess is "I do not know."

i'd like to see someone estimate their heat load of interior structure, drywall seems to be the biggest heat capacity source, but then again, the joist and floors might be right up there too. i found .67 btu/lb lumber, but thats as far as i got. as far as furniture, no real effect vs. total mass elsewhere.

i see the exterior mass as a sink where the interior is more of a source. as mike said in a stable condition, interior mass probably has little effect.

you might be right about wall being R and interior C.

Rich W

Hi gf



Yes, lots of good info here already. I have a 10yr old spice-like program that I use to do schematics and calculate loads. I'll try to see if this works. If not I can build the actual circuit on a breadboard. Once the objective becomes a bit clearer, we can decide on functionality/components of the device. I see many good analogies here already. What is your ultimate goal/use for this?

As far as actual loads, I liked the thread about real-time monitoring. I've lost more than a few hours of sleep over that- very well worth pursuing. I can see it as long-term diagnostic tool. Ex. High mass bldg with conditions a,c,d,e,l,p,r and t under X actual outdoor conditions has an effective efficiency rating of 90%. While a low mass bldg under the same conditions might be 80%. Manual J sort-of does this. It would be nice to see a database of real world variables working together. The more I think of it, the more variables/obstacles I see. This will be a huge job to implement correctly. What the heck, Herman Hollerith must have said the same thing awhiiiiile back. The tabulation's the thing my boy.

gasfolk

Steamed bacon?

Hi Christian,

Thanks for your sharp ideas (and for your delightful writing style).

I was dusting off my breadboard, but it sounds like Rich W (see above) may SPICE and/or breadboard this model. Spoke with the Dean (who is a professor of engineering) today, and he too is intrigued, so we could probably get lab time and perhaps (when they return in the fall) an undergraduate to help, but I hope Rich W will run with this and that discussion here will be useful to that end.

It would be great to start some kind of registry for folks to enter the measures of their own home, perhaps starting with Wallies who have done a Manual J, Eatherton Load, Boilerpro Load, and a (yet to be defined?) Thermal Mass, but such a registry would have to be started by someone with stature on The Wall.

S Ebels and Boilerpro both note the hazard of the Real Time method in buildings with high mass. Boilerpro wrote "you have to compensate due to thermal mass. A massive structure delays the full impact of low temps for a couple days." S Ebels' note suggests very high mass houses may require even longer observation. Interesting.

I will be interested to see how a steam boiler (not Kate Moss) affects this modeling.

Best regards,

gf

Christian Egli_2

Pictures of my models, aren't I lucky?

These models are not all that exotic, coal burning power plant are modeled everyday, a home is only an adaptation of this. We did it in school. Anyways, here are pictures of what an adequate model might look like. You'll see, I put my double doughnut coffee break to good use - and I had fun.

A capacitor filling with juice is nothing more than an ordinary bucket filling with water. The sort of stuff you'd do to entertain yourself at the beach.

Look at the first picture, Bucket Model of Steam System a, it shows a bucket, that's our home, it is full of heat, up to a desired temperature level. This bucket also has a hole at the bottom through which all our good heat will eventually leak out because of conduction, convection and radiation losses. The losses are to the environment.

You'll notice the simulated home is hanging by a rope that the hand of your favorite local TV weatherman is yanking up and down. As we know, the goal of home heating is to keep an acceptable steady indoor comfort. The goal here is to keep the water level in the bucket at a steady absolute level, you can reference it to the pulley.

If the bucket goes up, you've got to hope heat losses will allow you to dump enough heat so as to not cause overheating. If the bucket goes down, you'd want the boiler to come on quick enough to raise the level.

The boiler is merely a tap, it dumps heat. Boiler efficiencies do not really matter in this first simple simulation. (The last picture does take it into account, though.) The room thermostat I have represented keeps an eye on the water level and it calls for heat when needed. An outdoor reset system would have had the thermostat watching the TV weatherman, giving you a heads up on control time lag.

I labeled the first drawing as steam, but it is just because it heats with a radiator. Hot water performs the same way by dumping radiant (and convective) heat right into the objects to be heated and no where else. You can thus see the spout pours all its heat into the bucket without spilling over the sides. Cool.

Then there are the other bucket models that make all this very intuitive. The last one is for a radiant floor. The special aspect of this is the thermal inertia of the heating system itself that has to be taken into account. I have an extra bucket for the radiant system. In contrast, this is a particularity that does not apply to steam; this is why steam systems as a whole are top performing.

Things to keep thinking about are how the hole size changes everything, how the bucket volume has a drastic effect, and how the tap size changes the performance of the system. Think also about the thermostatic control.

But enough about steam, and gf steamed bacon does not do anything for me, you've probably found the one thing where a pressure cooker is useless... I find my bacon at its best cooked on the tinned surface of a copper pan. I like the very slight tackiness tin offers because it allows the bacon to stick flat while cooking. On non stick pans, because of the curling up, you don't get even results. Neither do you get crispy results when using an iron weight. The microwave oven works good but results are hard to control, you can't collect the fat and you've got to agree to the sacrifice of much paper towels.

That's model bacon. You had to ask didn't you?

My last drawing is of a more proper model. The bucket no longer is dangled on a rope. That previous simulation was not good for fully appreciating the dual effect the environment has: it hurts when it is colder outside and it helps when it is warmer. Heat can and does leak back into our homes.

Here the environment is another bigger bucket which connects to the others via a pipe that has the simulated resistance for insulation R value. This environment is your proper input because you can play with the water level to follow daytime / nighttime / summer / winter. The goal is to turn the boiler tap on and off in order to get the most steady and predictable home temperature level. Your output.

Tomorrow morning, while shaving, play with the faucet and the bathroom sink, make the level go up and down and convince yourself of how setback cannot cause increased fuel usage. Then, go have some bacon.

Regards

bob_46

Question?

If you have two identical(dead nuts) houses side by side. Same exposures, insulation etc. If you maintain both at 70F the heat loss will be the same. If you put a vessel in the center of one house that contains 1000gal of water how does that change the heat loss? bob

gasfolk

That's my question too...

Hi Bob,

I'm hoping someone can answer and would also ask how added thermal mass would change Ozian heat loss, boiler sizing, fuel use, and comfort? If allowed to choose one of the two houses, which should we take? If stuck with the other, would we be installing or removing that mass? If mass is good, how much will make a difference? 1000, 2000, 500 gallons?

Anyone?

I won't have a computer for the next week but will try to find access as much as I can, so please forgive my delays in responding.

Thanks,

gf

gasfolk

Follow-up questions

1) Does the above answer depend on the nature of the added mass?

2) Would 1000 gallons of water behave differently in a spherical tank versus a flat wall tank 1'x8.5'x16'?

3) Do some materials release heat faster than others?

gf

gasfolk

And finally...

How would you model this in a circuit?

jp_2

i'll give it a try.

one question about the 1000 gal tank? whats its temp? less than room temp its a sink, heat load Dt x 8,300lbs. 1000gal tank more than room temp, heat load -Dt x 8,300lbs.

bob, don't really understand 2nd part of question.

gasfolk, the container with the most surface area should gain and loose heat the fastest.

3.) you know the answer to this one, R value of material, or the heat conductivity of that material.

i'd call the tank a capacitor!

bob_46

Mass

I don't think the mass can have any effect on the heat loss. It could have an effect on comfort,whether or not it's good or bad depends. From an electronic point of view I think the mass would act like a capacitor..

jp_2

mass

i see mass useful only in solar designs, or wood stove/finnish stove heat.

jp_2

a little different.

I would catagorize a berm house different than a house with internal mass. the berm house is using "heat" from the ground to do the stabilizing, in a sense 'indirect solar'.

jp_2

internal mass & steady state

I'm thinking more and more that internal mass is not that much of a big deal, that is, in comparsion to the heat load of the house.

also anytime your supply and return temps are stead(constant circ,example)for any period of time, say over half an hour, I would call that a period of stead state. since your house stays nearly the same temp during the heating season, that tells you that you are never far from steady state, daily variance will be tracked by the heating system.

Christian Egli_2

Find flat leveled seasons, then heavy mass is easy and good

Which do you prefer pushing up a hill, a big 16-ton rock or just a two pounder? Same question again, which do you prefer having rolling down a hill right behind you? The 16-ton rock is a problem isn't it? But, of course, all the while you're pushing, if there is a sudden big gust of wind, your heavy rock won't take off on you and fly away.

Bob, the 1000 gal has no effect on the R-value hole size trough which your heat leaks out to the environment, that's obvious, but what it does do is dampen the speed at which temperature levels rise and fall within the home, you've added heat capacity.

This means you might not feel a sudden nighttime outdoor temperature drop, and it also means you have to pour more heat into the home to feel a desired temperature increase. Savings are not straight forward. It... depends.

Lastly, the home heat loss itself can be affected, that's the rate in BTU per hour BTU/h at which heat moves. This movement is directly related to the temperature differential between the inside and the outside. Now, if your big tank is causing a big difference in indoor temperature, it will also cause a big difference in the amount of heat loss.

Looking at the XF Electric Model drawing I posted higher

To model this tank, add yet another bucket (or capacitor) connected with a pipe (and the appropriate resistor) that leads to the central home bucket.

The 1000 gal will determine the C size of the bucket; the shape, the speed at which heat moves into and out of this tank, and the insulating value of the tank itself all determine the R resistance of the new pipe. The fluid level in the model will be indicative of the actual tank temperature.

Create waves in the environment tank and visualize what happens.

As far as personal preference, it all depends on what sort of climate you live in but high mass homes or the storage of high mass items in a warehouse are a real pain for adapting to seasonal changes in the spring and the fall. But, for adapting to daytime, nighttime changes, mass is very good.

bob_46

Christian

I like your models,especially the weather man idea. If both houses are maintained at 70F inside the deltaT from in to out is the same and heat loss is the same. As for mass I'm thinking the less mass the better. I had a few customers in Aspen with radiant in floor heat (high mass) that were very hard to control. It might be -20F at night and 45F by 10:00AM with large solar gain. Of course in this instance the heat emitter and the high mass were combined which is different than a tank of water. If set point is constant 70F I don't think the tank of water makes any difference. However if my wife lived in the house and was constantly changing the set point I think it is easier and faster to control low mass.

Constantin

I think it depends...

... please hear me out.

Thermal mass has the advantage of allowing you to harvest heat at one point and releasing it back into the home when it's needed. Some areas of the world (like parts of AZ or NM) experience massive daily temperature/insolation cycling, so mass can really benefit the home by smoothing out the high variability in weather conditions on a day to day basis.

If you go really high mass (like some earthships and that project in Canada), you can even take advantage of the summer/winter cycle. But not many of us want to live in earthships or go through the expense of boring out a thermal battery in the backyard (the Andrettis of the world excepted, of course).

Homes in areas that have little to no variability in terms of temperature or insolation will not benefit much from mass - unless you have a power cut. :-P

But more seriously, the AZ public utilities commission successfully tested a subdivision of high-mass homes that were only cooled at night, when the utility has excess generation capacity. Those homeowners could really take advantage of differential/peak demand pricing, etc.

jp_2

i agree,

high mass has advantages, but high mass and poor insulation makes for a real mess. with little insulation you are better off with low internal mass.