Reply
 
Thread Tools Search this Thread Display Modes
 
Old 01-08-2010, 12:54 PM   #29
Rivet Master
 
1973 31' Sovereign
Portland , Oregon
Join Date: May 2004
Posts: 1,245
Images: 22
Quote:
Originally Posted by Smartstream View Post
Malcolm, I really like the idea of radiant heat. I designed and installed a system in my house which happens to be a log house. I spent way too many hours under the house running tuning, both pex and copper. My heat source is a wood boiler outside by the wood shed.

I agree with kittrick, use a water to water plate heat exchanger and run antifreeze in a closed loop system. This will solve a bunch of issues with both freezing and keeping water in your tanks and domestic system and air in your radiant system. Even with the open system you are thinking about you will need a separate circulating pump as your domestic pump won't run unless a tap is open. With proper placement of your heat exchanger you might be able to take advantage of thermo-siphon and just use a single circulating pump.

An interesting set up would be to plumb the floor heat water directly to your water heater. Install a 5 or 6 gallon well insulated tank for domestic water and heat it with the plate heat exchanger. You now have two separate systems with your existing water pump providing domestic water and a circulating pump for floor heat with the only link being the heat exchanger. You can run the water temp hotter with a mixing valve on the domestic tank that will effectively give you more gallons from a smaller tank. During the summer you just valve off the tubing in the floor and the domestic water is heated through the heat exchanger rather than directly. There will be a small efficiency loss through the exchanger but I think it would be minor in the grand scheme of things. When plugged into 110 an electric element in the water heater could take care of both systems. I don't know what the electric capacity vs propane is on the new water heaters. By the way I heat my domestic water at home with a heat exchanger and thermo-siphon.

Like Gene said radiant heats objects not air. The aluminum inner skin will heat and cool rapidly, the cabinetry and upholstery not so fast. The logs in my house for example take a long time to heat soak from cold.

The BTU output of the forced air heater would be a good starting point for the heat loss of the trailer. After all heat is heat whether air or water, comfort is the big difference. I don't think you will see any big efficiency gains or losses. A few degrees up or down outside will have a greater effect. If you want a faster warm up then run more tubing. The greater the volume of water running through the floor, the more BTUs of heat will be transfered and the faster the warm up. The more important issue will be the recovery time of the water heater. Will it keep up with the heat being removed in the floor? I run my boiler water through a mixing valve so the floor supply is 130 and the return is about 100 to 110. It's not exactly like heating water from your tank at 50 or 60 to 110 for your shower.

As far as holding tanks go I don't know if running water over the top will bleed enough heat down to do any good. I would suggest running a tubing loop under the tank and cover the bottom with an insulation blanket. Any excess heat will wind up going up into the trailer where you want it.

Just a few things to think about but I think it is doable.
Good luck, Dan
It was my intent from the very beginning to have a separate pump for the heating system. In fact the one that I ordered is on the way. What I meant was that I thought that if I had a heat exchanger that I would need a second pump besides the fresh water pump. From what I have been able to tell with some minimum web surfing adding a heat exchanger and a second pump could add as much as $400 or even more to the overall cost of my system. That is more expensive than the water heater itself. How did you arrange your components for thermo-siphoning to work properly? That could reduce the extra cost associated with the heat exchanger. Do you have any good leads on small heat exchangers?

Since my trailer is so small I want to keep the system as simple as possible - both for cost reasons as well as for minimizing the space that the various component parts take up.

I have been intending to use a mixing valve for the domestic water on my system in any case so that the hot water in the tank could be hotter for the benefit of the heating system.

It could be a good idea to buy a water heater with an electric element. I had been thinking of going with a propane only model. Again partly for cost reasons.

It would be easy enough to run a heating loop under the tanks - at least for the waste tanks. It would be a bit harder to do so for the fresh water tanks. I am intending to put a foil blanket under them in any case. What I might think about doing is plumb in some way to add the loops if I determine that they are necessary. I would like to get something up and working and take some temperature readings here and there with the small hand-held infrared thermometer that I have. The main thing I need to do now is determine what type of water heater to get.

Malcolm
__________________

__________________
Only he who attempts the ridiculous can achieve the impossble.
malconium is offline   Reply With Quote
Old 01-08-2010, 01:41 PM   #30
Rivet Master
 
Over59's Avatar
 
1959 26' Overlander
Putnam , Connecticut
Join Date: Sep 2003
Posts: 3,064
Images: 37
I still like your original idea best.

As an optional alternative it should also be possible to install some sort of wall mounted radiators here and there that would be heated with hot water. There are some nice units, for example, that double as a heated towel rack that might work nicely.

However, you will need solar panels or a generator to keep that pump running in the wild. For my money the hot air furnance with a lower amp blower or two is the most direct solution, other than a couple cat heaters.

The trailer doesn't have a mass to store the heat and radiate it back to the peoples.. I thought thats how those systems work.
__________________

__________________
Over59 is offline   Reply With Quote
Old 01-08-2010, 01:48 PM   #31
Rivet Master
 
Smartstream's Avatar

 
1982 28' Airstream 280
Port Angeles , Washington
Join Date: Aug 2008
Posts: 1,371
Malcolm, The thermo-siphon is quite simple. Heat rises and cold sinks. Henry Ford used it on the Model T as there was no water pump. On my home unit the heat exchanger is under the water heater tank. As long as the water on one side of the exchanger is hotter than the other side heat will transfer and water will flow. The lower the exchanger is mounted in relation to the tank being heated, the faster the water will flow.

My heat exchanger is a FlatPlate that is about 8"x3" x2". It has 3/4" ports and flows plenty of water. I got it from Pex Supply for about $200. I'm sure its larger than you need but it's the smallest one they sell. Sendure, I think that is the name, makes many exchangers for marine use that come in all sizes. With a little creativity you can make your own out of copper tubing.

The challenge you will have will be your heating loops or zones. If the loops are not the same length, the water will only flow through the shortest loop, path of least resistance. In a home system this is controlled with zone valves and thermostats. In your trailer I would recommend keeping it simple with a single zone and running more tubing where you want more heat. Tubing runs under cabinets may be 12" apart while runs under floor in living areas may be 4" apart and sleeping area maybe 8". Adding tubing to control heat is much cheaper than valves and controls.
__________________
Smartstream is offline   Reply With Quote
Old 01-08-2010, 04:40 PM   #32
1 Rivet Member
 
kittrik's Avatar
 
1960 24' Tradewind
mount wolf , Pennsylvania
Join Date: Apr 2008
Posts: 17
Here is the info i came up with. Remember a radiant heat loss is differant than a air side heat loss(manual-J).
Assuming 2" batt insulation in the wall,cieling and floor. Single pane glass. I ran the design at 10 degree outdoor 68 degree indoor.
The radiant heat loss is 15,812 btuh. The max the floor can produce would be is 11,812 btuh using the 130 degree water temps. This would require 2-219' loops on 7" centers. This will give us a surface temperature of 82.9 degrees. The problem is this is based on using the entire floor area of the trailer. Because of cabinets, beds, etc we only have a small percentage of that floor for usable radiant heat. The tubing will contain 1.7 gallons approx 12lbs.
A company that i use for 12 circulatiing pumps is Laing.
I hope this is what you are looking for.
__________________
kittrik is offline   Reply With Quote
Old 01-08-2010, 05:41 PM   #33
Rivet Master
 
1973 31' Sovereign
Portland , Oregon
Join Date: May 2004
Posts: 1,245
Images: 22
Quote:
Originally Posted by kittrik View Post
Here is the info i came up with. Remember a radiant heat loss is differant than a air side heat loss(manual-J).
Assuming 2" batt insulation in the wall,cieling and floor. Single pane glass. I ran the design at 10 degree outdoor 68 degree indoor.
The radiant heat loss is 15,812 btuh. The max the floor can produce would be is 11,812 btuh using the 130 degree water temps. This would require 2-219' loops on 7" centers. This will give us a surface temperature of 82.9 degrees. The problem is this is based on using the entire floor area of the trailer. Because of cabinets, beds, etc we only have a small percentage of that floor for usable radiant heat. The tubing will contain 1.7 gallons approx 12lbs.
A company that i use for 12 circulatiing pumps is Laing.
I hope this is what you are looking for.
Thanks a lot for taking a look at this. This is getting me close to what I need to know and is a big help. I have a few questions for clarification:

1.) It is my understanding that foil insulation would behave better than fiberglass batt insulation in blocking radiant heat loss. Do you have some way of accommodating that in your calculations?

2.) What size PEX tubing were you calculating for? I was contemplating using 1/2".

3.) What about the flow rate you are assuming for the water? Presumably that would make some difference in the calculations too. The pump I ordered moves about 3.2 gallons per minute.

4.) I suppose I could run the loops closer together if that made sense. I had been thinking of using 6" on center initially.

5.) How much does the heat loss change for 20 degrees?

Thanks,

Malcolm
__________________
Only he who attempts the ridiculous can achieve the impossble.
malconium is offline   Reply With Quote
Old 01-08-2010, 07:07 PM   #34
Rivet Master
 
Smartstream's Avatar

 
1982 28' Airstream 280
Port Angeles , Washington
Join Date: Aug 2008
Posts: 1,371
kittrik, I find your calculations very interesting. Does your program consider percentage of area of built-in cabinetry vs open wall area? I suspect the percentage would be much higher in the AS but I don't know how much of an effect it would have on the total heat loss number. Also along the same line of thought how would the transfer of heat through the cabinetry from the tubing below compare to the transfer through the open floor area?

I was talking to a local contractor about a install he did. I was an industrial building about 200' on a side. It was being built for wood product manufacture with large machinery anchored to the floor. The fear of drilling through the radiant tubing was a concern. They wound up calculating the total length of tubing required and ran it side by side in about a 4' band immediately inside the exterior walls. This left the interior free of tubing to interfere with mounting machinery. This was a concrete slab floor and the end result worked perfectly.

I mention this because in Malcolm's case he needs more tubing in open floor areas. I realize the air space between floor and sub-floor is not as efficient as the concrete slab but will he gain much by adding more tubing or simply overheat the floor? Also will there be much of a gain putting more tubing under the cabinetry? Another option might be some finned baseboard heat exchangers if there is enough wall space to do so.
__________________
Smartstream is offline   Reply With Quote
Old 01-09-2010, 11:53 AM   #35
Rivet Master
 
Gene's Avatar
 
2008 25' Safari FB SE
Grand Junction , Colorado
Join Date: Sep 2007
Posts: 10,840
Malcolm, I guess you're right about the air purger and expansion tank, but maybe I suggested that subconsciously because I think I'd want a closed loop. If you're good with copper, it seems not too hard to build a heat exchanger yourself (easy for me to say).

I was thinking "why not put tubing under the cabinets"? Then I realized a lot of food gets stored in them and would get slow cooked at 130˚ (Airstream as crock pot?). Otherwise, heat under cabinets and furniture seems like a good idea because they would store a lot of heat, but you may have to be careful what you keep in them. Would a bed get too hot? Maybe fewer loops under them and more under the floor.

And are you planning to run loops around the water tanks? They would be necessary for camping in the colder months, but difficult to drain the loops. It seems there would be several low points in those loops, perhaps unintended. This seems like another plus for a closed system.

Gene
__________________
Gene is offline   Reply With Quote
Old 01-10-2010, 08:15 AM   #36
1 Rivet Member
 
kittrik's Avatar
 
1960 24' Tradewind
mount wolf , Pennsylvania
Join Date: Apr 2008
Posts: 17
1: The foil has a better u-value but only when it can directly "see" radiant.
When it is in walls, etc its r-value is about the same as batt insulation.

2: I used 1/2" pex size
3: 3.2 gpm is tooo fast. the water will not have a chance to give off any heat. I use 1 gpm.
Remember radiant heat only heats the objects. Putting it under the cabinets is only going to heat the bottom of the cabinet. Till that heat gets to the air it will be way under the temps required.
It appears we can do a good job of floor warming the exposed areas but not enough to heat the space.
Did you mention you had the inner skin off? Run the tubes up and down the walls with foil behind them and turn the entire shell into a convector!!
__________________
kittrik is offline   Reply With Quote
Old 01-10-2010, 01:03 PM   #37
Rivet Master
 
Wabbiteer's Avatar
 
1973 27' Overlander
1972 29' Ambassador
St. Paul , Minnesota
Join Date: Apr 2006
Posts: 1,912
Images: 2
Blog Entries: 2
Sorry I'm late to the thread! Before WE get too far down the merry path... with this level of complexity all the shortcomings of time constraints and language rear their roaring heads, I'm not able to do much more than add comment and observations so I apologize in advance if quick and easy is not in my vernacular.

Maybe think sectional/modular raised flooring - or wall panels - instead of subfloor installation? Sure, heat loves to rise but mucho energy will be conducted outdoors via the spars and frame instead of through the flooring, anything less than perfect insulation will not stop it. With wall-panel radiant panels maybe adding a liner's liner to match those sexy brushed aluminum interiors of the new Airstreams could work well; even a dual action of radiant and convection of air behind them?

Looking at the heated water recovery rates between gas & electric listed for Suburban heaters - NOTE: they list INPUT BTU's of propane, not output - and comparing the two (2440 watts required to match gas rate) I calculate all their units are expected to be about 69% efficient when new. That is a lot of $$ of heat chasing out of the flue, adding additional heat exchange method would help but the extreme simple inlet/outlet design injects hazards.

After day-dreaming for years about Takagi jr propane instant water heater being used as baseboard and radiant heat source I am gathering pieces to clone the aqua-hot system...

Aqua-Hot Heating Systems Inc.

To make the required 'buffer' tank for looping domestic water / space heating / heat source input (and don't forget spare loop to add solar water heat) the sky is the limit to where to locate it - I plan on removing the nasty & leaking fresh water tank in my 1973 and using part of that area under the galley counter for a home-made buffer tank - and use the current refrigerator space/access door/venting opposite the galley counter to house the burner and pumps.

As to pump sizing - the important part is heat differential in/out of the heaters coils - In my case not what is being drawn from central tank - the 3-gallon-per-minute pump is measured with little or no line restriction or head pressure. I've committed to using 3/4-inch supply lines everywhere using this diesel heater and will be counting on trial & error zoned thermostats for even heat distribution...

Anyhow - time constraints now, will check back in later.
__________________

Wabbiteer is offline   Reply With Quote
Old 01-10-2010, 04:39 PM   #38
Rivet Master
 
1973 31' Sovereign
Portland , Oregon
Join Date: May 2004
Posts: 1,245
Images: 22
Quote:
Originally Posted by kittrik View Post
1: The foil has a better u-value but only when it can directly "see" radiant.
When it is in walls, etc its r-value is about the same as batt insulation.

2: I used 1/2" pex size
3: 3.2 gpm is tooo fast. the water will not have a chance to give off any heat. I use 1 gpm.
Remember radiant heat only heats the objects. Putting it under the cabinets is only going to heat the bottom of the cabinet. Till that heat gets to the air it will be way under the temps required.
It appears we can do a good job of floor warming the exposed areas but not enough to heat the space.
Did you mention you had the inner skin off? Run the tubes up and down the walls with foil behind them and turn the entire shell into a convector!!
I had the inner skins off but unfortunately that is in the past tense now. They are all back on now except for the middle strip down the center of the ceiling. I also have the rough framework of my inner walls, shower and cabinets in the way now. Putting the tubing in the walls seems like a pretty interesting idea though. I am not opposed to the idea of adding some tubing in places where it might be visible. I had also given some thought to adding some tubing behind an aluminum overlay of some sort somewhat like the various kinds of wall radiators that are available.

Perhaps using some other type of tubing on the wall or ceiling areas that looked better than PEX tubing might be better. Maybe aluminum or copper tubing would be a good idea. I suspect that both aluminum and copper would make better radiators than PEX tubing.

The challenge is to find some visually appealing and reliable way to attach tubing to the walls or ceiling in a way that conducted heat to the inner skin so as to make it a radiant plate in my heating system. I do still want to keep the overall cost down too by the way.

Back on the topic of whether or not I can get enough tubing in the floor though. Is there any practical reason why I couldn't run tubing closer together in the areas of the floor that are exposed? What if I ran the tubing at say 3" on center for example? Given your calculations how many feet of 1/2" tubing would I need total to overcome your calculated heat loss?

I am going to have to see if I can still cancel the order that I placed for my hot water pump. If not I will be stuck with fixed speed 3.2 gallons per minute pump. Maybe this would be OK though if I made two or three separate tubing loops? Wouldn't the flow would be divided into however many branches therefore effectively reducing the flow in any given branch to closer to 1 gallon per minute? I did by the way look at Laing pumps as was impressed by the one on the following page:

East Coast Solar :: Laing D5 VARIO Bronze PV-Direct Circulating Pump $169.90

This one is not only cheaper than the one I ordered but has a variable flow adjustment which seems like a good idea.

Back on the question of water flow rate though I am having a little trouble understanding why a faster flow rate than is necessary would be a problem other than that it might use more electricity to run the pump. Isn't heat going to transfer to the PEX based on the temperature of the water passing by rather than being based on the rate of flow?

Thanks for all your help,

Malcolm
__________________
Only he who attempts the ridiculous can achieve the impossble.
malconium is offline   Reply With Quote
Old 01-10-2010, 05:46 PM   #39
Rivet Master
 
ROBERTSUNRUS's Avatar

 
2005 25' Safari
Salem , Oregon
Join Date: Mar 2006
Posts: 7,268
Images: 18
Blog Entries: 51
Quote:
Originally Posted by malconium View Post
Perhaps using some other type of tubing on the wall or ceiling areas that looked better than PEX tubing might be better. Maybe aluminum or copper tubing would be a good idea. I suspect that both aluminum and copper would make better radiators than PEX tubing.


Back on the question of water flow rate though I am having a little trouble understanding why a faster flow rate than is necessary would be a problem other than that it might use more electricity to run the pump. Isn't heat going to transfer to the PEX based on the temperature of the water passing by rather than being based on the rate of flow?

Malcolm
Hi, I know nothing about radiant heat or floor heating systems, But I do know that if you use a non-contact thermometer on your car/truck you will see a higher temperature reading on the metal thermostat housing and a brass radiator tank that you will see on a rubber radiator hose or a plastic radiator tank. This tells me that for heat transfer, you would be better off using copper tubing.

Too fast of flow rate in a car radiator can cause overheating because it doesn't have a chance to transfer the heat. This could be the same in reverse for your system.

Do you plan to loop all of the tubes or parallel them? I heard somewhere that after so many 90 degree turns [unknown number] in plumbing the fluid pressure drops to zero.
__________________
Bob

2005 Safari 25-B
"Le Petit Chateau Argent"
[ Small Silver Castle ]
2000 Navigator / 2014 F-150 Eco-Boost / Equal-i-zer / P-3
YAMAHA 2400 / AIR #12144
ROBERTSUNRUS is offline   Reply With Quote
Old 01-10-2010, 06:55 PM   #40
Rivet Master
 
1973 31' Sovereign
Portland , Oregon
Join Date: May 2004
Posts: 1,245
Images: 22
Quote:
Originally Posted by ROBERTSUNRUS View Post
Hi, I know nothing about radiant heat or floor heating systems, But I do know that if you use a non-contact thermometer on your car/truck you will see a higher temperature reading on the metal thermostat housing and a brass radiator tank that you will see on a rubber radiator hose or a plastic radiator tank. This tells me that for heat transfer, you would be better off using copper tubing.

Too fast of flow rate in a car radiator can cause overheating because it doesn't have a chance to transfer the heat. This could be the same in reverse for your system.

Do you plan to loop all of the tubes or parallel them? I heard somewhere that after so many 90 degree turns [unknown number] in plumbing the fluid pressure drops to zero.
I appreciate your feedback...

Your observations with the rubber hoses and metal parts of an automobile cooling system do give some good collaboration to what I was thinking abut the metal tubing. I believe that a materials suitability for the purpose that I have in mind is at least in part related to the conductivity of the material. It may somehow be related to the thermal capacity of the material as well I suppose.

I am going to have to think a bit more about the flow rate issue.

My thought is to loop the tubing. Partly for practical reasons. PEX can only bend just so tight around a corner without having to resort to a fitting. Radiant heating systems try to avoid fittings whenever possible. That is an interesting issue with the 90 degree bends that I have not heard before. Does anyone else reading this thread know about that?

Thanks,

Malcolm
__________________
Only he who attempts the ridiculous can achieve the impossble.
malconium is offline   Reply With Quote
Old 01-11-2010, 06:57 AM   #41
Be Calm, Have a Cupcake
 
Secguru's Avatar
 
Vintage Kin Owner
Houston , Texas
Join Date: Nov 2007
Posts: 223
Images: 1
A few questions...

1 - What is the total volume of water that will be in the lines under the floor?
2 - What is the total weight of the system including the water in the lines?
3 - How does that added weight change your gross weight and available payload?
4 - How will you heat the water tanks if reflective foil is between the water lines and the sub-floor?
__________________
Secguru

Would you rather have a mansion full of money or a trailer full of love?
Secguru is offline   Reply With Quote
Old 01-11-2010, 09:11 AM   #42
Rivet Master
 
Gene's Avatar
 
2008 25' Safari FB SE
Grand Junction , Colorado
Join Date: Sep 2007
Posts: 10,840
Malcolm, I have heard you have to calculate bends when figuring out flow rate and pump capacity. My guess is 90˚ bends would be more restrictive than curves and sharp curves more so than gradual ones. Putting the Pex 3" apart may be much too close because of the tight bends. Like Bob, I know nothing about this. I'd start by checking the internet. Maybe Lowe's or Home Depot have books on installing this kind of system with tables explaining it.

Gene
__________________

__________________
Gene is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Using the heat pump/heat strip instead of furnace. crazylev On The Road... 38 10-28-2016 08:58 PM
DEAL!!!Minor Heat Damaged exterior Airstream eBay Watch Airstreams on eBay 0 10-04-2009 12:40 AM
Are there calculations to work out solar sytems ArticJack Generators & Solar Power 1 10-04-2008 09:40 PM
Generator Calculations? BigD Generators & Solar Power 8 04-08-2007 09:14 PM
Airstream new web page: BIG loss to us? femuse Our Community 28 03-30-2003 07:45 PM


Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 05:11 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.