Bus Conversions dot Com Bulletin Board
August 22, 2014, 04:39:10 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
News: This BB is intended for the sole purpose of sharing conversion and bus related information among visitors to our web site. These rules must be followed in order for us to continue this free exchange of info. No bad mouthing of any business or individual is permitted. Absolutely no items for sale are to be posted, except in the Spare Tire board. Interested in placing a classified or web ad, please contact our advertising dept. at 714-903-1784 or e-mail to: info@busconversions.com.

   Home   Help Forum Rules Search Calendar Login Register BCM Home Page Contact BCM  
Pages: 1 2 3 [All]   Go Down
  Print  
Author Topic: Pex & hot water question  (Read 3615 times)
rayshound
Full Member
***
Offline Offline

Posts: 164




Ignore
« on: June 22, 2007, 06:50:20 PM »

I am installing my webasto plumbing now. I'm using pex for the baseboard radiators & for & engine warmer. I had put a red dot front dash a/c & heat out of an airport shuttle bus in my mci.  My question is do I hook the dash heat to the webasto or to the engine. I had removed the old lines for bus heat. Could I use pex to hook dash heat to engine? Pex rated at 180 degrees f @ 80 psi.  Engine psi <15 psi.  I appreciate some thoughts on the idea.  Thanks Ray
Logged
Jerry Liebler
Hero Member
*****
Offline Offline

Posts: 1320




Ignore
« Reply #1 on: June 22, 2007, 06:58:47 PM »

If you are using pex for a hot water heating system it's strongly advised that you use the type that has an oxygen barrier in it.  The reason for the barrier is to reduce corosion of iron and steel portions of the hot water heating system, this is not a concern with domestic water systems.  I kept the defroster on the engine coolant system thinking I'll need it many times when I don't need the Webasto and don't want to wait for the Webasto's coolant to heat up.
Regards
Jerry 4107 1120
Logged
Nick Badame Refrig/ACC
1989, MCI 102C3, 8V92T, HT740, 06' conversion FMCA# F-27317-S "Wife- 1969 Italian/German Style"
Global Moderator
Hero Member
*****
Offline Offline

Posts: 4860


Nick & Michelle Badame


WWW
« Reply #2 on: June 22, 2007, 08:12:31 PM »

Hi Ray,  How are you?

Jerry has a point about the OB Pex. Question, if you are parked, will you be able to run the dash fan inconjunction with the Wabasto without draining your start batts?

If thats a concern, then I would keep the dash system seprate and let the engine heat it.

Good Luck
Nick-
Logged

Whatever it takes!-GITIT DONE! 
Commercial Refrigeration- Ice machines- Heating & Air/ Atlantic Custom Coach Inc.
Master Mason- Cannon Lodge #104
https://www.facebook.com/atlanticcustomcoach
www.atlanticcustomcoach.com
rayshound
Full Member
***
Offline Offline

Posts: 164




Ignore
« Reply #3 on: June 22, 2007, 09:05:13 PM »

Thanks that makes sense. Would using pex from engine to dash heat be o.k. or to hot?  Thanks Ray
Logged
Don4107
Sr. Member
****
Offline Offline

Posts: 407





Ignore
« Reply #4 on: June 23, 2007, 12:02:21 AM »

I have not finalized the plan yet but I want dash heat from both the engine and Webasto.  Why, all that glass.  It lets in a lot of heat when hot out and looses a lot of heat when it's cold.  It may be more complicated than useful, but I have been working on the design anyway.
Logged

Don 4107 Eastern Washington
1975 MCI 5B
1966 GM PD 4107 for sale
1968 GMC Carpenter
Sojourner
Guest

« Reply #5 on: June 23, 2007, 01:51:54 AM »

Whatever you choose…make sure your heated water supply flow is great enough to get the BTU you need in the worse condition. At least 1” ID hose or pipe or tubing from engine and then reduce to fit exchanger unit..

Suggest to always connect to engine as well diesel heater in series with return line from dash heater to inlet and 2 way valve to by-pass front dash exchanger. Its primary purpose is to heat engine and/or interiors. If want to heat potable water…get a marine heat exchanger build into electric water heater. Another word a marine heater with 2 inlets & 2 outlets.

FWIW

Sojourn for Christ, Jerry
Logged
Nick Badame Refrig/ACC
1989, MCI 102C3, 8V92T, HT740, 06' conversion FMCA# F-27317-S "Wife- 1969 Italian/German Style"
Global Moderator
Hero Member
*****
Offline Offline

Posts: 4860


Nick & Michelle Badame


WWW
« Reply #6 on: June 23, 2007, 03:48:58 AM »

Thanks that makes sense. Would using pex from engine to dash heat be o.k. or to hot?  Thanks Ray

Ray,

One thing you would have to concider, if you were to have an overheating problem, you can get as hot as 210 deg's before your engine
would cut out, and then at that point it could go another 10 deg's up before cooling down.
Heat PEX would be a better choice in my book. My Oxygen barrier PEX is rated at 250 deg's.
Nick-
Logged

Whatever it takes!-GITIT DONE! 
Commercial Refrigeration- Ice machines- Heating & Air/ Atlantic Custom Coach Inc.
Master Mason- Cannon Lodge #104
https://www.facebook.com/atlanticcustomcoach
www.atlanticcustomcoach.com
Gary '79 5C
Hero Member
*****
Offline Offline

Posts: 613




Ignore
« Reply #7 on: June 23, 2007, 04:01:30 AM »

I would like to re-ask the point Sojourner made about installing the Webasto piping to route hot water thru the cabin heaters, and the engine block,( hot water heat exchanger).
Are there any problems/ downsides to doing this. I see one obvious problem and that is there is many additional hoses & connections any of which could leak and shut down the engine with loss of coolant.
Other than that I am fine with it, This set up has served me well. I do see that Dick Wright sells ( and reccomends) a SS heat exchanger to "separate" the engine coolant system, but still share the heat.
This system is great upon waking up in freezing temps outside, I and my engine are warm and cozy.

Enjoy your weekend folks,
Gary
Logged

Experience is something you get Just after you needed it....
Ocean City, NJ
edroelle
Sr. Member
****
Offline Offline

Posts: 351


1998 Royale Prevost




Ignore
« Reply #8 on: June 23, 2007, 05:45:47 AM »

Jerry is right.  Use large piping.

Heat exchangers between the Webasto and the bus engine are usually recommended.  I did not do it that way.  I did not see a problem in eliminating this component other than the failure mode - if a line ruptures and you lose your coolant.

I used the original bus lines and tied-in my Webasto in the front.  I valved the lines so that I could bypass the engine, or the living area heat exchangers.  Thus, the Webasto, or the bus engine, could heat the living area and/or the heat exhanger in the hot water heater.  This also allowed for the Webasto to preheat the engine.

When I shut-off the valve to the engine, I just shut the one valve at the right rear, to prevent flow.   (The valve in the center of the bus engine compartment is also hard to access.)  By leaving one of the two valves open, allows for coolant expansion such that an additional Webasto coolant tank was not necessary.

Design your system on paper so that the coolant flow makes sense.

Ed Roelle
Flint, MI
Logged
rayshound
Full Member
***
Offline Offline

Posts: 164




Ignore
« Reply #9 on: June 23, 2007, 08:04:45 AM »

Thanks everyone great info, now let me really push the envelope with this question. If I use say the 1" hot pex to run from the engine to the dash heater in my mci-8 the old floor a/c duct I had removed and added unistrut and had run several conduits from front to rear. The duct isn't covered yet & plenty of room but when I lay down the plywood access is gone. could I use 1&1/4" or 1&1/2" conduit with the long radius bends to run the 1" pex in and use as a "chase" ?  That way any future problems I could pull the pex out to replace. Would the conduit get to hot? Do you think it would sweat? Would it be better to run the pex in plastic water pipe. I would not have the long radius 90 degrees. Thanks Ray
Logged
Nick Badame Refrig/ACC
1989, MCI 102C3, 8V92T, HT740, 06' conversion FMCA# F-27317-S "Wife- 1969 Italian/German Style"
Global Moderator
Hero Member
*****
Offline Offline

Posts: 4860


Nick & Michelle Badame


WWW
« Reply #10 on: June 23, 2007, 08:38:58 AM »

Ray,

When you said you removed all the orrigianal heat lines in your first post, I guess you don't still have them?

Nick-
Logged

Whatever it takes!-GITIT DONE! 
Commercial Refrigeration- Ice machines- Heating & Air/ Atlantic Custom Coach Inc.
Master Mason- Cannon Lodge #104
https://www.facebook.com/atlanticcustomcoach
www.atlanticcustomcoach.com
edroelle
Sr. Member
****
Offline Offline

Posts: 351


1998 Royale Prevost




Ignore
« Reply #11 on: June 23, 2007, 09:52:30 AM »

Conduit is OK.  I used inexpensive black flexible polyethylene (Home Depot water pipe) as conduit in that tunnel area - front to back, and to systems bay.

Ed Roelle
Logged
rayshound
Full Member
***
Offline Offline

Posts: 164




Ignore
« Reply #12 on: June 23, 2007, 10:59:41 AM »

Nick, yes I cut all the a/c & heat lines. Over kill I guess but I really cleaned out the chase. I removed floor, removed plywood in a/c duct floor & steam cleaned the tubings, and removed all the above mentioned. I had to cut into sections to get out. I por15 everything, used pour foam on the 4 wheel well areas and am presently running new a/c & heat lines in the a/c tray using two layers of unistrut & several plastic conduits from engine area to the nose wheel well. I know the lines could have been reused but they were so very large & went to condenser bay & to dash. I would rather run new & correct size. I'm also rerunning new fuel lines (copper) with & extra just for a purge line to the fuel processor.
                                        Thanks again any more suggestions welcomed as now is the time soon the new floor will br liquid nails & screws.   Ray
Logged
rayshound
Full Member
***
Offline Offline

Posts: 164




Ignore
« Reply #13 on: June 23, 2007, 11:04:59 AM »

Ed. thanks for the reply. When you said you used the black plastic lines in the tunnel, did you run pex inside of it? Thats my thoughts on this is to use the grey plastic conduit with the long radius bend & run the hot pex inside of it to protect the pex and have a way to mount the pex & replace the pex at a later date if needed. I'm thinking 1&1/2" conduit to run the 1" hot pex in would have plenty of room. Thanks again. Ray
Logged
edroelle
Sr. Member
****
Offline Offline

Posts: 351


1998 Royale Prevost




Ignore
« Reply #14 on: June 23, 2007, 06:13:43 PM »

I did not run Pex.  I ran the polyethylene for wiring and 4 aught battery cables and grounds. 

I see no reason that you could not do the same for Pex.

Ed Roelle
Logged
Sean
Geek.
Hero Member
*****
Offline Offline

Posts: 2547


'85 Neoplan Spaceliner "Odyssey"


WWW

Ignore
« Reply #15 on: June 24, 2007, 12:00:37 AM »

I would like to re-ask ... about installing the Webasto piping to route hot water thru the cabin heaters, and the engine block,( hot water heat exchanger).
Are there any problems/ downsides to doing this?


Gary,

I recommend separating the systems using a heat exchanger.

In addition to the reason you already identified (more possible points for engine coolant to leak out, possibly causing an engine problem), here are a few more:

(1)  Coolant expense:  Your Webasto (or other brand) diesel boiler and the rest of your hydronic components, such as fan heaters, are very tolerant of a wide range of coolant types.  I use Prestone, but almost any brand or color of coolant, automotive or diesel, will work fine -- use the cheap stuff from Wal-Mart.  As opposed to your main engine, which is very picky about its coolant, requiring special diesel coolant formulation, and regular testing and addition of SCA's.  Much more expensive stuff, and if you have a single system, you'll need to fill the whole thing with this more expensive coolant.

(2)  Coolant changes:  Your hydronic system likely will only need coolant changes every five years or so, possibly longer.  It's a closed-loop, mostly sealed system, whereas the engine coolant is subject to contamination from microscopic migration paths through the head gaskets, and metals migrating into the coolant from high-speed circulation and cavitation issues.  You'll need to change engine coolant on a much more frequent schedule, and, again, by having a single system, you'll be changing roughly twice as much (or more) coolant each time, depending on expansion tank size (and do remember you need an expansion tank on your hydronic system).

(3) Head pressure and flow issues with the engine water pump:  Depending on the size of your hydronic system, it may be asking an awful lot of your engine coolant circulation pump (the "water pump") to try to circulate through the entire system.  You'll likely have to add a boost pump, which will then have to run every time you have the engine running (unless you have a set of valves to bypass the hydronic system).  And then you'll be heating your hydronic system every time you drive, whether you need to or not.

(4) Pump sizing for the hydronic system:  Again, with a single system, you'll need to pump the coolant through the whole engine system every time the system operates, so your electric pump for running the hydronic system while parked will need to be that much bigger (or have that much more back-pressure and wear and tear).  And, don't forget, you'll need to take steps to make sure the engine-cooling thermostat stays closed when the boiler is running (i.e. make sure the 'stat operating temperature is higher than the operating temperature of your hydronic system) -- otherwise, you'll end up paying to heat the outdoors as your precious hydronic fluid flows through the radiators!

(5) Heat-up time for the hydronic system:  When you come home to a cold coach and flip the hydronic system on, it takes a while for all the coolant in the system to come up to operating temperature before your fans will kick on and give you heat.  Having a single system will increase this time, because there is more fluid to heat up and because the coolant is flowing through a cold metal engine block.  You'll have less waste and get heat and hot water much faster by having separate loops.

Almost all the advantages of combining the systems can be achieved with a simple heat exchanger and addition of one small electric pump, to circulate the engine coolant when you want to "pre-heat" the block for cold-weather starts.

We have separate loops, yet still get all the heat and hot water we need while rolling down the road using our heat exchanger.  In fact, we get good heat and hot water for an hour or two after we park without starting the Webasto, just from residual engine block heat and the thermal mass of the system.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com
Logged

Full-timing in a 1985 Neoplan Spaceliner since 2004.
Our blog: http://OurOdyssey.BlogSpot.com
Gary '79 5C
Hero Member
*****
Offline Offline

Posts: 613




Ignore
« Reply #16 on: June 24, 2007, 04:32:21 AM »

Sean,
Thanks for the response to me and others, I agree with all that you have presented, and all are tradeoffs as what someone wants to achieve.
Now the disclaimer, I purchased the bus, did not design it.
The coolant costs would be less expensive for the heater loop and longer changes, no doubt.
I do have a solenoid valve which opens when the Webasto loop calls for heat, thus some what isolating the bus loop. Good to know to turn down the T'stat if a leak is discovered within the coach on the road.
You are correct that it takes a long time to warm the coach with the engine. For now this fits our style of travel and use of the coach.
I think I will get the dimensional data from D. Wright and locate a spot for installation. I believe the cost 2 yrs ago was under $500 for a SS unit. My Webasto is located within the engine comp. curb side. I have good access to it, engine and the air compressor etc.
I also am looking at replacing the elect. water heater with a elect./exchanger unit.
Thanks for the input as your's is valued along with others on the board.

Enjoy your sunday.

Gary
P.S. I have several RV'er friends in the office and when they ask about my "Partridge Family Bus" conversion, I email my coach pic's and your site as to just what can be done.
Logged

Experience is something you get Just after you needed it....
Ocean City, NJ
belfert
Guest

« Reply #17 on: June 24, 2007, 09:06:29 AM »

Flat plate heat exchangers are available for way less than $500 even in stainless steel.  Check Ebay for these.
Logged
Don4107
Sr. Member
****
Offline Offline

Posts: 407





Ignore
« Reply #18 on: June 24, 2007, 09:17:06 AM »

Sean,

Is your hydronic loop pressurized?
Logged

Don 4107 Eastern Washington
1975 MCI 5B
1966 GM PD 4107 for sale
1968 GMC Carpenter
NewbeeMC9
NewbeeMC9
Hero Member
*****
Offline Offline

Posts: 1162


1981 MC9 8V71, HT 740




Ignore
« Reply #19 on: June 24, 2007, 09:33:00 AM »

Another option that opens up with an Isolated system is the posibilty of using the same loop and fans for cooling, Chill water system using the same distribution system that u have for heating.

be sure to have drains for condensate at the inside HX

Do it your way!!  then post pics! Smiley
Logged

It's all fun and games til someone gets hurt. Wink
Sam 4106
Hero Member
*****
Offline Offline

Posts: 645





Ignore
« Reply #20 on: June 24, 2007, 12:19:02 PM »

Hi Rayshound,
You mention using grey PVC electrical conduit for a chase for the pex heating line. Are you aware that PVC will get soft and deform when heated? I called our neighbor, an electrical contractor, to ask at what temperature the deformation will start but he couldn't give a specific temperature. He did say that at 180 degrees it would sag unless it is supported along its entire length and that if it is firmly attached, such as to unistrut, expansion will also cause deformation. Something you may want to consider before you buy it.
I don't know why you want to use two materials, PVC and pex, to accomplish a job that could be done with copper tubing and a short hose or pex at each end. I know that copper is expensive but one length of copper may not cost more than two lengths of plastic.
Good luck with whatever you choose to use. Sam 4106
Logged

1976 MCI-8TA with 8V92 DDEC II and Allison HT740
Dallas
Guest

« Reply #21 on: June 24, 2007, 01:25:59 PM »

Sam,

Copper prices have sky rocketed in the last year or two.
4' of 1" copper is now $29.75 at Plumbing Supply.com and it was only about $8 3 years ago.

100' of Therma PEX is $124.24 at Outdoor Stove Supply.com

Plus, PEX can be run in long lengths without unions or other joints and can make mild bends that copper can't.

I prefer copper too, but with todays prices, it just ain't worth it.
« Last Edit: June 24, 2007, 01:27:43 PM by Dallas » Logged
rayshound
Full Member
***
Offline Offline

Posts: 164




Ignore
« Reply #22 on: June 24, 2007, 06:21:23 PM »

Thanks Sam, that was the info I was looking for, not happy but thats the way it is. I may be able to run pex in hot pvc pipe. I don't know if just running the hot pvc pipe would be o.k. Thanks Ray
Logged
belfert
Guest

« Reply #23 on: June 24, 2007, 06:28:55 PM »

How about FRP pipe instead of PVC pipe for a conduit?  I suspect it would hold up to more heat, but you would have to do more research.  FRP pipe should be available at a good plumbing wholesaler.  No home improvement place will have it.
Logged
Gary '79 5C
Hero Member
*****
Offline Offline

Posts: 613




Ignore
« Reply #24 on: June 24, 2007, 06:39:03 PM »

Ray,
Another thing with the PVC Conduit is that even if supported well, the thermal expansion will make long runs "grow" in length. Also causing the appearance of sag. Sam 4106 is right on with his thoughts.

Good Luck,
Gary
Logged

Experience is something you get Just after you needed it....
Ocean City, NJ
rayshound
Full Member
***
Offline Offline

Posts: 164




Ignore
« Reply #25 on: June 24, 2007, 06:43:37 PM »

Thanks Gary, I guess another approach might be just run the pex and anchor with some approved "pex" anchor or bracket. I mainly wanted to run a "chase" to run the pex in to get where I won't be able to get to again. Ray
Logged
belfert
Guest

« Reply #26 on: June 24, 2007, 07:12:12 PM »

I used some WATTS WaterPEX brand clamps/anchors for the PEX pipe for my domestic water.  I would assume they can be used for radiant heating too.

See http://www.watts.com/pro/_products_sub.asp?catId=70&parCat=530
Logged
rv_safetyman
Hero Member
*****
Offline Offline

Posts: 2199


Jim Shepherd


WWW

Ignore
« Reply #27 on: June 24, 2007, 07:16:11 PM »

Wow Ray, you are getting great input!!

I have the Aqual-Hot with three zones.  I plumbed one zone to the living area and one to the bathroom/bay.    We found that, even in really cold weather, we could do without the third circuit in the bedroom.

We used that zone to plumb to the big Red Dot in the front.  That provides heat and defrost (does a really great job!!).  The Aqua-Hot heat on the road is mostly provided by the engine, so it is like having the engine heat the Red Dot. 

However, it goes it one better.  We got caught in 1 degree weather on our way to Bussin' 2007.  When we woke up, we had a thick sheet of ice on the inside of the windshield.  I turned on the Red Dot and within a few minutes, the windshield was clear (and the engine was warmed a bit).

The Aqua-Hot folks really tried to talk me out of this arrangement.  I think they were worried about liability if something happened to that circuit, or the Aqua-Hot failed and we would be without defrost.  I really am not worried about that event.

For the run from the Aqua-Hot to the Red Dot, I used some very high quality heater hose (industrial quality). 

The heat going down the road is great, as is the defrost.  That may be hard for a guy who lives south of Houston to understand Grin

Jim
Logged

Jim Shepherd
Evergreen, CO
’85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
Blog:  http://rvsafetyman.blogspot.com/
rayshound
Full Member
***
Offline Offline

Posts: 164




Ignore
« Reply #28 on: June 24, 2007, 08:50:20 PM »

Thanks Jim I appreciate it. Lot's of good info. Ray
Logged
Sojourner
Guest

« Reply #29 on: June 24, 2007, 10:11:36 PM »

If you choose hose of any kind that going thorough very hard to access to without conduit…. Then when it sprung a leak, you will have to hope everything is going smoothly pull out old hose while new replacement hose being pulled with-it. However with metal or PCVC (cream colored & for hot water temperature) use for conduit. Worrying about expand & contraction? ….either use rubber sewer connection hose with ss clamps at every long length or leave one end of long straight conduit floating thorough a large home made grommets (3/16” ID fuel line hose with a long single cut slit so it go over metal hole’s edge) hole in metal panel. Or use rubber links from muffler shop with 2 metal hooks & ss clamp onto one loose end of conduit to hang. The other end is fasten to chassis or framing or panel.

I would strongly advise to use stiff type of water line such as copper tubing unless it has unavoidable elbow in conduit. Any hose will deteriorate quicker than copper tubing except when frozen. If you use copper tubing… slit 2” long rubber heater hose to slip over tubing & vinyl tape it  to keep it in place while pulling thorough conduit, to avoid vibrating noise inside of conduit.

Another advantage having conduit is it will control water or coolant spray leakage from getting into no no areas.

FWIW

Sojourn for Christ, Jerry
Logged
DavidInWilmNC
Hero Member
*****
Offline Offline

Posts: 594


1978 MC-8 as I bought it May 2005




Ignore
« Reply #30 on: June 25, 2007, 07:05:45 AM »

I think I would use copper.  I realize it's more expensive initially.  It won't be as expensive if you offset its cost by replacing the PEX or whatever material you use.  If you use PEX inside conduit, won't there be a lot of rubbing between the two?  There's no real way that I know of to suspend the PEX inside the conduit and still have it removable, which is your goal.  There will be quite a bit of mass inside that 1" PEX pipe that will cause motion from the bus' movement.  I'm not sure that a 1" PEX pipe slapping around inside another pipe would be such a good idea.  I know price is a concern, but with all the trouble and expense you've already gone to, it just doesn't make a lot of sense to skimp here.  I've always heard "If you want it cheap, use PEX.  If you want it to last, use copper".

David

Logged
Sean
Geek.
Hero Member
*****
Offline Offline

Posts: 2547


'85 Neoplan Spaceliner "Odyssey"


WWW

Ignore
« Reply #31 on: June 25, 2007, 01:35:56 PM »

Is your hydronic loop pressurized?


Umm, I'm not sure how to answer this.

The coolant is not under pressure while the system is at rest.  But, as with most coolant-loop systems, there is an expansion tank at the very upper-most part of the system, which is, itself, a pressure vessel.  It has a pressure cap on it similar to the one on an automotive radiator.  There is also about a 6' height difference between the top level of coolant in the tank, and the lowest point of the system, which means that, even at rest, the low point is at a static pressure of roughly 17psi.

When the system is in operation, the "boiler" heats the coolant to somewhere around 200° Fahrenheit.  I put quotes around the term, because, while hydronic heaters are often called diesel-fired boilers, the intent is not actually to "boil" the coolant, meaning to cause it to change state from liquid to gas.  (That being said, if the circulating pump stops, this is exactly what might happen. The boiler, whether Webasto or some other make, will have high-temp cut-out safeties to protect itself from overheating in this case.)  One reason you should use "antifreeze" coolant mix in the system, as opposed to plain water, is that the antifreeze raises the boiling point of the coolant, from 212° to around 265°, making actual boiling of the coolant less likely in the event, for example, of low circulation in the system.  The actual temperature your system will reach is one of the design parameters, controlled by a thermostat (sometimes called an "aqua-stat") in the coolant loop which causes the boiler to switch on or off.

As the temperature of the entire system rises, the "partial pressure" of water vapor and even antifreeze vapor in the expansion tank will rise, as well as the air pressure in the tank as the air, eventually, will also heat up to nearly the design temperature of the system.  At this point, the Ideal Gas Law takes over  -- as long as the pressure cap stays on the tank and does not open, the pressure of the air/vapors in the tank will rise as the temperature rises.  Because it is, at this point, a closed system, that gas pressure will be transmitted to the coolant and will increase the operating pressure of the whole system.  To protect the system from hose ruptures or worse, the pressure cap on the expansion tank has a relief valve that opens at a specific pressure,  just like an automotive radiator.

Even if the system were open to atmosphere at all times (which would decrease the thermal efficiency), the circulation pump also causes a pressure difference.  In addition to the static pressure mentioned above, the operation of the pump will cause a dynamically lower pressure on the input or "suction" side of the pump, and a dynamically higher pressure on the output side.  Calculation this pressure difference is a matter of fluid dynamics, the math for which is way more than I want to do on a bulletin-board post.

Long-winded, but I hope I've answered your question.

Incidentally, contributing to the materials discussion, I think PEX is a bad choice because it is not rated for the temperatures and pressures that the system MAY encounter should there be any kind of malfunction.  Our system is entirely plumbed with 1" diameter silicone "heater" hoses with solid (non-perforated) hose clamps.  All valves, nipples, lead-ins, etc. are copper or brass rated for hot water.  While copper pipe would also work, long runs of copper pipe will be subject to significant length changes due to thermal expansion, and the thermal conductivity of the copper will mean you will lose a lot of heat to the environment as compared to hoses, unless you insulate them.  Plus, hose is generally easier to run.  It used to be more expensive than copper, but, with copper skyrocketing, I'm not sure any more.  FWIW.

-Sean
http://OurOdyssey.BlogSpot.com
Logged

Full-timing in a 1985 Neoplan Spaceliner since 2004.
Our blog: http://OurOdyssey.BlogSpot.com
Sam 4106
Hero Member
*****
Offline Offline

Posts: 645





Ignore
« Reply #32 on: June 25, 2007, 04:20:36 PM »

Hi Dallas,
I don't think buying  copper in 4' lengths is realistic for ray" needs. If you buy anything in short lengths or small quantities you always pay dearly. As an example, I needed 30 3/16" lockwashers today. They were 5 cents each or a box of 100 for $1.49. Similar savings can be had by buying copper tubing in 100' coils. Since Ray will need two runs nearly the length of his bus it doesn't seem unrealistic to buy a 100' coil. As you well know anything made from oil and it's derivitives has also gone up in price, maybe not to the extreme of copper, but I'll bet the cost of PVC and Pex are also higher than a few years ago. Admitedly, I have not checked prices for any of these materials.

Rayshound,
If you are set on using Pex in a chase, maybe electrical metalic tubing (EMT) would work for you as a chase and it can easily be clamped to your unistrut.
Good luck, Sam 4106
 
Logged

1976 MCI-8TA with 8V92 DDEC II and Allison HT740
Jerry Liebler
Hero Member
*****
Offline Offline

Posts: 1320




Ignore
« Reply #33 on: June 25, 2007, 04:47:42 PM »

Sean,
    Methinks you've made a bit of a misscalculation.  Six feet of water column doesn't create 17 PSI, much closer to 3 PSI, and with the 5 PSI pressure cap the Webasto's coolant pressure should be under 9  PSI under all conditions.
Regards
Jerry 4107 1120
Logged
Sean
Geek.
Hero Member
*****
Offline Offline

Posts: 2547


'85 Neoplan Spaceliner "Odyssey"


WWW

Ignore
« Reply #34 on: June 25, 2007, 08:21:35 PM »

...    Methinks you've made a bit of a misscalculation.  Six feet of water column doesn't create 17 PSI, much closer to 3 PSI, ...


Sorry, I tend to think in absolutes, not relative -- atmospheric pressure at sea level is, of course, 14psi, so the pressure differential (aka "gauge pressure") is, you are right, 3psi.

Quote
and with the 5 PSI pressure cap the Webasto's coolant pressure should be under 9  PSI under all conditions.


Agreed, which is why I hemmed and hawed about the answer... it's not really under pressure, by most standards, but technically, it is a pressurized system.  Also, be aware that there are different release pressures for these caps, and the one that comes with the expansion tank may or may not be the correct setting for your system.

-Sean
http://OurOdyssey.BlogSpot.com
Logged

Full-timing in a 1985 Neoplan Spaceliner since 2004.
Our blog: http://OurOdyssey.BlogSpot.com
Pages: 1 2 3 [All]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.18 | SMF © 2013, Simple Machines Valid XHTML 1.0! Valid CSS!