Midnight Brilliant Heating Idea! (or maybe not?)

[John61CT]

So what fuel are you burning?

I believe Espar and Webasto can go either way, and I guess you know they're pricey

 

[Redbearded]

I like the idea of using Paraffin as the source for heat storage and taking advantage of the phase change of the material for the added energy storage capacity. In looking at the heat storage capacity and the factoring in a usable phase change temperature I could see that holding a nice bit of heat.

the units get a bit wonky here, but bear with me

Heat for us is simplest in BTU (at least to compare to standard heaters). If using paraffin (the one I found at HobbyLobby has a melting point of 133 deg F which would correspond to paraffin -26 carbons) that would leave a heat of fusion of 256 kJ/kg to convert to BTU/lb we need to 

256 kJ      1 BTU .     1 kg .      110.3 BTU
-------- * ---------- * --------  = -----------   of paraffin (this is only for the phase transition)
  kg        1.055 kJ .   2.2 lb .      lb


so that in addition to it's normal heat capacity which for a low melting paraffin is about .659 (Btu / (lb * F))

If a batch of paraffin was taken from 50 deg F to 150 deg F and had a weight of 40 lbs we could expect 

(100*40*.659)+(40*110.3) = 2636 + 4412 = 7048 BTU which is equivalent to an 800W electric heater for about 2.5 hours.

So backtracking for a bit here we would need roughly 

[font=STIXGeneral,]100x[font=STIXGeneral,](0.659[font=STIXGeneral,])[/font][font=STIXGeneral,]+[/font]x[font=STIXGeneral,]([/font]110.3[font=STIXGeneral,])[/font][/font][font=STIXGeneral,]=[/font][font=STIXGeneral,]2730 (heat output from 800w heater for 1 hour)[/font][/font]

Which leads to about 15.5 lb of paraffin for 1 hour equivalent heat from an 800W electric heater (assuming you get to the system to 150 F and it drops to 50 at night, and no losses... lol) 

When I get my trailer built I will plan on measuring the power input to interior temp comparison, but it would be interesting to see what other ppl think of using a small heater for their rigs.

p.s. if you see any errors in my calcs, let me know... with all the units and conversions + being rusty, there could be errors.

 

[Redbearded]

If getting the heat into the paraffin is an issue you can add 20% by wt graphite and still retain ~90% of the thermal properties. Not sure if that will be needed yet though.

 

[Redbearded]

using the same thing for water is 

100*40*1= 4000 BTU for the same temp and situation.

So on a weight basis the paraffin is roughly 70% more energy storage capable in our working temp range, though it's practical use is less.

 

[John61CT]

Are you talking about kerosene?

IMO if not carrying propane, the only option left is the fuel used by your generator and/or propulsion engine.

IOW diesel or gasoline.

I guess kero and diesel are pretty close.

I would use off the shelf heaters, not try to build my own.

 

[Redbearded]

John61CT

The idea is to see if it is possible to design around the need for fossil fuels in the trailer. I know it may be an exercise in futility, but it gives me something to think on

I'm talking about using the paraffin as a medium to store heat directly from the sun and also using the excess solar PV production for heating the paraffin as well. This paraffin would then be used, by way of a heat exchanger in the tank to heat water running through the floor of the trailer distributing and releasing the heat that was stored during the day. It would also be used to provide hot water from the same system. I'm thinking about running the fresh hot water through the same heat exchanger as the radiant floor water.

The calculations are to see how much paraffin I would need to carry and it's equivalent heating potential compared to a standard small electric heater. There are a lot of assumptions, but I at least now know that I can make something function and the paraffin has a greater capacity to store heat when compared to water (at least at the temp range we are working in).

 

[Redbearded]

I found some Thermodynamic panels for using a refrigerant like R134A in Link which could be interesting

Here is a pic of a heating loop though I will use the paraffin in place of the water then run a second heat exchanger in the top portion and split that off for the hydronic heating system and for hot water in the trailer. 

 

[WanderingCanuck]

For such a small space, does it make a big difference whether you use in-floor pipes vs. forced air circulation? I'd think that a forced air heat exchanger would be much easier to implement, less costly, and less prone to messy failures (and difficult repairs). Think about putting your storage tank inside a very well insulated container, but with air circulation around the tank. Now circulate air through the space under control of a thermostat. Use some actuators to open/close baffles if needed. I like simple, or at least "simpler".

I didn't verify your math (not my thing) but it looks like a good starting point for an experiment. I'll probably refer back here when/if I do some of my own experiments.

 

[John61CT]

The idea is to see if it is possible to design around the need for fossil fuels in the trailer. I know it may be an exercise in futility, but it gives me something to think on

Aha, thought experiments are fun, even full-fledged Science Projects if you get that far.

In my case I want to be able to boondock in snowdrifts, so we'll need our dino juice.

 

[Redbearded]

WanderingCanuck

In my mind the difference between the use of in floor heating vs forced air comes down to the ability to contain the heat. If I heat the air in a space, then open the door in such a small space it will cause much of the heated air to disperse. If I heat the floor I have a built in radiator that can reheat the space more quickly. At least that is what I'm envisioning. I know of the places I have been in, the forced air heating feels like it cycles more, and leads to drafts, whereas places with floor heat tended to be more comfortable. I remember reading some studies about it, but here is a pic

The other thing I'm thinking about is I want hot water anyways, so this is kinda two for one. I design a system a bit more complex, and accomplish hot water and heating with little inputs except the sun. and it looks like I have a strip about 1.5 feet wide on the side of the trailer which would be about perfect for some of the thermo panels

 

[Redbearded]

So I've been doing some more research and it looks like someone is doing this already for homes. I have a bit more research to do, but it looks similar
https://www.sunpump.solar/

 

[highdesertranger]

my buddy's house in New Mexico is heated that way. it works good however during the winter it must be run 24/7 if you shut it down for any reason it takes forever for it to catch up and heat the house. also when you get a leak it's a huge pain in the ass. they have had a few leaks. highdesertranger

 

[Knit]

Most people want heat at night and early in the morning. Not a very good match for solar thermal. I second desertranger’s comments. The problem with radiant systems and most heat pump systems is that they work best when on for long periods of time and they cannot recover quickly. In my case, I sometimes want a bit of heat just in the morning to get to the coffee pot. A propane furnace works great to put out higher temperature warm air for a shorter period of time.


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