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RV Maintenance
Thermal Efficiency



Patricks-Sun700.JPG, 35 kB
Patricks Point State Park
I took this picture at Patricks Point while we were safe, dry, and warm in our RV.
Now this is RVing; When you can look out and see this!
But, you need to know what the insulation in your walls is doing, and what your furnace is doing. And other things too.

RULERYEL.GIF, 4.2kB
Thermometer_Full7.jpg, 52kB
Here is my "calibration" thermometer, and I use it for all the following measurements. It is fast to react, but not as fast as modern electronic types. I love and rely on my old antique thermometer.
Thermometer_Cusp5.jpg, 29kB
It is an alcoholic thermometer as you can see by the red color. The alcohol line forms a bottom cusp, and a resulting curve that is concave up, indicating vanderwall attraction, as is the case with alcohol and glass. Alcohol "wets" the sides of the glass and climbs up. This is to say that the internal forces of cohesion of Alcohol are less strong than the external adhesive forces to glass. Mercury, on the other hand, sticks to itself more than glass, forming the opposite curve: a convex line. You always read at the cusp wether it is up or down. In this example: 76.9F degrees.
HeatC-Image.gif, 73kB
RULERYEL.GIF, 4.2kB

Air Furnace Heater
(Losses)

I have a huge panoramic picture window on the back end of the RV at the dinette. It is beautiful. That big window is one reason why we bought it, but it carries a large heat liability. To compensate for all the glass, I have Pleated Fabric Shades on all windows except two. I have modified the top Valances and extended side Jambs for less clearance. Great R-values in the walls, or anywhere else, are useless, and will have little effect on the R-value of the RV as a whole unless you address the window issue.

The Keystone is a cheap RV. Despite all the cheap construction, it does have a good, entirely enclosed underbelly, with fiberglass insulation, and simi inclosed fresh water holding tank. Keystone claims R-7 sidewalls, R-11 roof, and a R11 floor insulation.
In addition, I have started modified the RV with radiation reflecting bubble mylar, styrofoam board, and carpet under cabinets and in the holds.

But this page is more about measuring, and being able to see the progress...



RULERMAR.GIF, 1 kB
WaterHot-Pict.JPG, 20 kB
Air Furnace on left, Water heater on right.
Here are some recorded measurements.
During this run, one window was cracked about one inch open for ventilation.
During this time, there was frost on the ground with humidity high, and it was just getting light, Outside temperature was 27F degrees, climbing to 30F degrees.
I recorded when the heater came on or off.
The Time, Inside Temperature, The duration, Outside Temperature, Decay Temperature.
6:53 off                      27F   
7:07 Onn  66.1F  (14Min off)  28F
7:13 Off  72.3F  ( 6Min onn)  28F
7:27 Onn  66.3F  (14Min off)  28F  Decay 6.0F
7:33 Off  72.0F  ( 6Min onn)  29F
7:47 Onn  65.9F  (14Min off)  29F  Decay 6.1F
7:54 Off  72.2F  ( 7Min onn)  30F
8:09 Onn  66.0F  (15Min off)  30F  Decay 6.2F
8:15 Off  72.6F  ( 6Min onn)  30F


BBALLBLU.GIF, 0 kB Furnace Ran 3 times in 0.933 hrs. Each cycle lasts 0.311 hours.

BBALLBLU.GIF, 0 kB The off-time is, on average, 14 minutes.

BBALLBLU.GIF, 0 kB The on-time is, on average, 6 minutes.

And there are a couple of timed functions that also have nothing to do with outside or inside temperatures:
BBALLBLU.GIF, 0 kB 90 seconds out of every on-time is devoted to cool-down.
Reclaiming and scavenging residual heat from the "burn".
BBALLBLU.GIF, 0 kB 22 seconds out of every on-time cycle is devoted to pre-run, (15s Purge and 7s ignition).
Initially, old air must be purged out to prevent explosions.
90 seconds plus 22 seconds is 1.9 minutes.
Total cool down is 14 minutes plus 1.9 minutes is 15.9 minutes.
BBALLRED.GIF, 0 kB Therefor the on-time, "burn time", for heat production, out of the measured 6 minutes, is 4.2 minutes, 0.07 hr.
Total burn time is 0.07*3/.933 = 0.225 hr.
(For battery usage, it is the full 6 minutes.)

So for any group of hours during the day...
Battery Duty cycle = 6/(14+6) = 0.30 Onn/time
Propane Duty cycle = 4.2/(14+6) = 0.21 Onn/time
Summation of 12.6 minutes per hour of burn
Summation of Rest periods is 47.4 minutes per hour.
So for an outside temperature of 28F degrees, the heat is on not quite a quarter of the time to maintain a steady state inside temperature.



HeatDecay.gif, 46kB
The red dot points are when the Furnace came on.
The blue dot points are when the Furnace turned off.

As you can see, my RV is not insulated good enough; I would be freezing by nightfall, not to mention water lines.


RULERMAR.GIF, 1 kB
BANASTAR.gif, 1.5kB This is how you are to build it:
The ark is to be three hundred cubits long, fifty cubits wide and thirty cubits high.

Genesis 6:15
RV Interior Living dimensions: Width=8.0ft, Height=6ft 8in, Length=17.0ft
Surface area is two end walls, two side walls, and a celling and floor.
Surface area = 2(8ftx6.66ft)+2(17ftx6.66ft)+2(8ftx17ft)= 605sqft

Average inside temperature is aprox 69F degrees
Outside temperature is aprox 29F degrees
Average 40F degree difference between outside and inside, (steady state).

My RV will have an average R-Value:
Furnaces are rated for input BTU.

AirSpecksSF20.jpg, 15 kB
AirFurnace-76.jpg, 16 kB Manufacturer document has 76% efficient.
Efficiency:
There are some furnaces at 75%, and some at 95%.
Your furnace will be in between somewhere.
According to this sticker, mine is 76%. Mine is rock bottom, and evidently, outside wildlife enjoy and share it's use too.
And that explains why the wildlife like to huddle up against my RV more than my neighbors RVs.
Eq-Q-Energy1.gif, 13kB Eq-Q-EnergyRval.gif, 11kB
Steady-State condition:
The delta Temperature is 40F degrees (nearly steady state).
This method requires the temperature deference to be constant.




The above determination of the R-Value was by direct measurement.
"A steady state condition of a set amount of energy input, and a set temperature difference between inside and outside." (Actually, the inside temperature is zig zagging between 72F and 66F, but it has a steady state workable average.)
This empirical measurement is for the whole RV in one go.
Or...

RULERMAR.GIF, 1 kB
You can take the average of all the specific R-Values of all the construction materials:
(For example, Springdale claims it has R-7 Sidewall, R-11 Roof, R-11 Floor Insulation)
I will call this the itemized method.

BBALLBLU.GIF, 0 kB Front EndWall is 8.0ft by 6.66ft = 53.3sqft
Front EndWall (no windows) is 53sqft at RVal=7.

BBALLBLU.GIF, 0 kB BW-Window.JPG, 3 kB Back EndWall 34sq ft at RVal=7
Glass 19.3 sqft at RVal=0.8, and 19.3sqft of Pleated Blinds at RVal=1.

BBALLBLU.GIF, 0 kB RW-Door.JPG, 3 kB Right Wall is 6.66ft by 17.0ft=113sqft
Right Wall is 88.8 sqft at RVal=7
Glass 12.3sqft at RVal=0.8
Door 9.2sqft at RVal=5, Plastic 2sqft at RVal=2, Al Frame 1 sqft RVal=0
Right Wall contains a door 25.5 in wide, 69in high, 1 in thick styrofoam with plastic window and 1 inch aluminum frame with direct exposure to inside.

BBALLBLU.GIF, 0 kB LW-WinBack.JPG, 4 kB Left Wall is 105 sqft at RVal=7
Glass, two windows, 7.8 sqft at RVal=0.8
Refrigerator
Open window 0.5 inches: 0.8sqft at RVal=-20

LW-WinFront.JPG, 3 kB
BBALLBLU.GIF, 0 kB Roof is 8.0ft by 17.0ft=136sqft
Roof is 127sqft at RVal=11
SkyLights 4 sqft at RVal=2
BathRoom Vent 1 sqft at RVal=.1
AirConditioner 4 sqft at RVal=.1
AirConditioner was not layered with insulation yet. Also room air was leaking into roof compartment
BBALLBLU.GIF, 0 kB Floor is 8.0ft by 17.0ft=136sqft
Floor is 136 sqft at RVal=11

Eq-Sum.gif, 5 kB
Add up every glass window, Air Conditioning on the roof, Plastic Roof vents, styrofoam metal door, etc. A6 is simply the RV skin area. All six surface areas: four sides and a roof and a floor.

Eq-RVall-SpecificWalls.gif, 19 kB
The specific fiberglass estimates are from Keystone.



The measurement method falls short of the materials and claims of Keystone.


RULERMAR.GIF, 1 kB There is another approach: By looking only at the temperature decay during the 14 minutes.
We are only looking at a part of one cycle: the decay cycle.
This approach concerns Entropy and the natural process of energy dispersal.
I have already derived this equation elsewhere.
GRNL.gif, 3 kB Heat Entropy
So now, I just present it here again as evident and previously established.



Eq-Temp1.gif, 21kB
BBALLBLU.GIF, 0 kB Initial Inside temperature starts out at 72.3Fdegrees,

BBALLBLU.GIF, 0 kB And decays to 66.1F degrees

BBALLBLU.GIF, 0 kB in (14) t minutes.

BBALLBLU.GIF, 0 kB Static Outside temperature is aprox 29F degrees,


Knowing k, we now have a complete formula for calculating how long to wait for any temperature.



RULERMAR.GIF, 1 kB
Eq-kR-Dimension.gif, 20kB
I suppose k could also be equated to R-val...
I was thinking k can only depend on Surface Area A, Initial stored heat Q, and RVal.
There is nothing else in there!
Probably, k=A/(QR).


From looking at the diminsions, it looks possible.
The dimensionality is 1/t.
But it looks too simple...

Eq-Q-Energy1.gif, 13kB
OK, I will take a chance. I will guess at it...
For this method, we will consider the intire energy produced in one hour. Which should be more accurate than a mear 14 minutes. Also, there is a lot of latent heat comming from the duct work in the 14 minutes that has not been accounted for in only 14 minutes.
Eq-Q-EnergyRval.gif, 11kB
The R-Value is easy as it is just by definition...
The R-Value is the reciprocle of how much energy is going through the wall surfaces, and the floor and cealing surfaces. And that is also Per degree differance between those surfaces.
Eq-Q-EnergyNewt.gif, 42kB
Now, to actually calculate the Decay Time Constant... If we insert Q into the k time constant equation we go nowhere. The equation says are units are correct, and that is about it. We are substituting the furnace BTUs in twice, and all it does is cancell out.

But what we really want to do is look at the stored residual heat from "things", after the big furnace is shut down. Forget about the furnace; we don't care about it anymore. If the furnace is gone, we truely have the Decay Equation in essense. The reserve heat stores, together with the insulation, will begin a slide of temperature down a precise cooling path. And THAT is the real equation we are discribing.



Interisting...
Can't really get there from here. But at least we can get the mC Product. The temperatue will decline not from insulation alone. But from also the mC Product: my canned goods, and my water bottles, the wood walls, the metal refrigerator and stove, and even the very air inside.

Another time, I calculated ths mC value as 144. I must have had more Cambels Soup on board. As I make physical changes and work on my RV, it is going to change according to the physical construction.

This has been more of an exercise in finding the mC Product, than as the original quest, of finding the k Decay Time Constant. Can't find it from just this...


I have a lot of work to do to keep from freezing to death. Cause the Rval is not so good...


RULERMAR.GIF, 1 kB
"If lessons are learned in defeat... our team is getting a great education."
- Murray Warmath / Minnesota


HeatedBelly.jpg, 13 kB There may be a "heated belly"!
Two ducted heat sources!
But, I am not sure if this hose exists in my Springdale.
You might check yours.

#12 is a separate heat outlet for heating the underbelly.
#12 is a 3inch hose.
And yes! When I stick my hand down under the floor above the fiberglass, there IS extra heat. I did not count on this sneaky stuff.
#3 is the rigid heating ductwork of which my calculations are already familiar.


I like the concept of #12 because the 5/8 flooring is going to retain a lot of heat. Instead of the concept of the wood flooring as an added insulation, I would rather have it as a source of specific heat.

But, then again, I would have to insulate the frame. Can not do that. Thinking...


RULERMAR.GIF, 1 kB

Air Heater
Consumption



AirHeatCoolDown.JPG, 16 kB Batteries:
From the same data as above:
The heater came on approximately 3 times an hour at 6 minutes each.
That is a duty cycle of 0.3: a third of the time.
18 minutes out of every hour.
Battery consumption = 18min * 7.5Amps = 2.25 Amp/Hr
Expected life on one 100 Amp/hr battery:
100/2.25 = 44 hours, not quite two days.
Therefore, one battery without replenishment, will not make it through the second night at 28F degrees outside.
(With good sunshine there are no electrical restrictions, and the gap from day to day is easily bridged.)


LPG Propane:
20,000 BTU/Hr Air Furnace consumption
Two 7 gal tanks, 30lbs of gas
1 gal has 91,502 Btu, 21622 btu per pound
640,514 BTU per tank
640000/20000=32Hr with Furnace continually on
Worst case scenario is 28F degrees continuously day after day. Duty Cycle=.21: Life=120Hr, aprox 5 days per tank at 28F degrees outside.

With any kind of sunshine through the windows, this should go to a nice round figure of 7 days/tank: One week
But that does not include hot water or cooking. Along the coast for a week of boondocking, with temperatures around 50F degrees, we use at most a half tank. This is with pleasant and normal usage, and one tank per week would be the extreme.
RULERMAR.GIF, 1 kB

KitchenSinkUnderInsulate.JPG, 28 kB Under the kitchen sink. The under side of sink is a fascinating yellow translucent with sun exposure on top.
Seems to me it is more efficient to heat "things" in the RV than to use the same "things" as insulators. Do not use the inside partition walls to insulate; instead, use them to store energy. Do not go directly to heating the air, but instead heat intermediary things such as the bath tub, commode, metal stove, canned goods, wooden barriers, and kitchen sink. They can be heat reservoirs. Ultimately, the air will still be heated, which was the final direct result anyway; it just takes longer. The ultimate fate of the heat is unavoidable. However, To get the same outside wall insulation, I added some reflective insulation in inconspicuous places, like under the sinks. Because with the original scenario, the inside wall partitions did offer some indirect insulation, such as when closing the bathroom door and shutting cupboards. Primarily, the function of the outside walls as insulation remains the same.
Thermal Heat Capacity
Specific enthalpy
Specific heats:
Copper     0.39 KJ/C/Kg 25 ft service cord, The cord is massive and compensates for its low Specif Heat.
Fiberboard 2.2  KJ/C/Kg Bed supports, Storage walls.
Glass      0.84 KJ/C/Kg Dishes in pantry
Steel      0.49 KJ/C/Kg metal Stove, metal PowerCharger
Paper      1.3  KJ/C/Kg Magazine storage
Wood, oak  2.0  KJ/C/Kg Some cosmetic parts of walls
Wood, pine 2.5  KJ/C/Kg Some inside partition walls
Water           KJ/C/Kg Canned goods, bottled water
Run Drier hose from central air duct to under the stove. The hole through the floor under the stove is not visible. From there the air goes to inside cabinetry for all canned goods and kitchen sink. Also, water distribution lines are at a hub for right side of trailer.

Run Drier hose from central air duct to under the bath tub. The flooring hole under the bath tub is not visible. From there the air goes to bathroom area, under bathroom sink, water pump, water lines, Charging center, and finally up through a clothes closet.
Also water distribution hub for left side of trailer. RULERMAR.GIF, 1 kB
Filter-Heat-Insulate.jpg, 20 kB
Finished insulating the two areas that hold water lines, pump, and filter with Reflectix.
The refrigerator sits above these two areas on half inch ply. I installed insulation on the top of both areas. The high ridge in the back is from the wheel finders. It is made of steel with a carpet covering. I insulated this too. The back wall is hard board with RVal-5 fiberglass behind. I installed carpet then reflective insulation over that too. All outside surfaces have better insulation now. The left and right compartments do not go to the outside, so no insulation is necessary. In fact, inter-compartment wood holds heat. It is a good thing! This wood can be used as a reservor of heat energy, With warm wood around, it will take longer for the lines to freeze. In addition, I drilled large holes between all inner compartments so that heat will be distributed. To the right, is an unseen compartment that is under the bathtub. I directed heat from the flooring to come up into this compartment. Heat flows from the bathtub compartment through holes into the water pump compartment which, as you can see, also has a lot of water lines and a water filter. The water pump compartment generates it's own heat, but access to furnace heat also helps. There are also holes to the left into the next compartment which is a power supply compartment.


RULERMAR.GIF, 1 kB LeakyHoses.jpg, 13 kB All - every single one - of these factory hoses had to be replaced. They all either had an occasional drip to massive leaks. Factory crimps do not stay tight. But these lines can be repaired:
HackSaw the band at an angle. Then hacksaw radially at the bulge ring. Remove as much of the band as possible. Then apply a new adjustable band. But the other end will eventually leak too. Better to just replace the whole thing with vinal and then you are done forever.
The replacement ends are not "finger-tights" as these factory hoses. They require some real torque, but never leak.

However, I have never checked vinal for "drinking water safe".


RULERMAR.GIF, 1 kB I started using Reflectix when I found it in Osh. And cheap. AT 2 ft wide, it runs about a buck a foot. 5/16 inch thick, and reflective both sides. It has an RVal of 1.1 for thermal conductance, and a radiant RVal anywhere from about 2 to a whopping 20, depending on clear air space on the reflecting side, and on wave length of the heat.
For example at room temperature and at a half inch clear, the RVal is 2.7.
A 0.75 inch free air space above the reflecting side, the RVal is 3.8. If you have many inches, the RVal can be 20.
That stuff is for me! In some tight spaces, I am not able to exploit the stuff to its full potential.


AirCond-Insulation-Wrong.jpg, 34 kB
And in one application, for the air conditioner, I have the heat going in the wrong direction. I have the reflecting surface facing up, and heat is not allowed into the RV. Instead, I would prefer to have room heat reflected back down and conserved. And heat loss increases linearly with temperature. So, high up near the ceiling the temperature is hottest. That is where there is the greater tendency for heat loss. That is true for contact transmission. And it is even worse for Radiation: it is to the fouth power! Gotta keep the ceiling insulated.

The product can even work both ways (both sides), but I could not see a practical way, and still have the air conditioner functional and workable. I have never really used this new air conditioner. Perhaps I should just block it off.

I plan to never use this air conditioner. I have used it only once, and that was only because the dealer gave me a free night at a Redding park, where the temperature was over a hundred degrees. I don't know about the RV, but I was not designed to be in Redding California. The air conditioner works good, and it should! It is as a new unit, but I will never use it. It is just a big old wind resistance when going down the road, and an avenue for cold when resting on the coast. And these two facts make it look bad, wether going down the road or not.

Anyway, too bad the reflecting side is facing up.
RULERMAR.GIF, 1 kB

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