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Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 12:27 pm
by Shadow Catcher
I have spacing constraints, very tight in the compartment where the water heater is. I am thinking some way to burp the system, with out getting water all over the place :roll:

Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 1:53 pm
by MtnDon
Our trailer has no problems with the pump we have starting.

I think if you placed a tee fitting just before the pump and installed a valve in the leg of the tee that should be sufficient to bleed off the air and get some water to the pump. I had a similar issue years ago and that solved the air locking, non-priming of the pump in that situation.

Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 2:44 pm
by ELM
Shadow Catcher wrote:I have spacing constraints, very tight in the compartment where the water heater is. I am thinking some way to burp the system, with out getting water all over the place :roll:


This is how it's done some cars with a high heater core. http://www.blauparts.com/assets/vw_timi ... _step1.jpg
How it works is you loosen the hose clamp and pull the hose back to line up the hole in the hose with a hole in the tube and let the air bleed out and when fluid comes out you slide the hose back on and clamp it.

Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 4:44 pm
by Shadow Catcher
I may be able to put a bleed screw in the top hose and let the camper pump fill the hoses. Need to finish the install before I borrow trouble.

Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 4:58 pm
by lrrowe
In essence that is what I do, but not intentionally. I use the house pump to charge the water lines and force the air out when I turn on the shower facuets.

Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 6:04 pm
by Socal Tom
lrrowe wrote:Same here. My pump is lower then the hot water tank exit. No priming needed. I used it this week for a 4 day outing at VA Beach with a TearJerker event and it worked perfectly. I turned the heat down to 64 for the night and all was great.
My next modification will be to put a rheostat on the fan to slow it down and maybe one on the pump so the hot water will flow through the heater more slowly thus maybe reducing the propane used.

Also my air flow has slowed down. Seems like I broke one of the fan blades last fall and had to purposely break off one on the opposing side to balance things out. That for sure reduced the air flow.


The best way to slow the water flow would be a needle valve upstream of the pump. This will also reduce the power used by the pump. On the other hand a rheostat will probably increase the power used.
FWIW, slowing the water flow is unlikely going to reduce the propane load. The propane is being used because you have taken BTUs out of the water, and the amount of BTUs needed won't change based on the flow rate of the pump. However, if you lower the speed of the pump, then you might reduce the rate at which the BTUs are removed ( the BTU transfer is most effeient when the air temp and water temp are farthest apart) and potentially use more propane, since you would spend more time sending cold water into the tank, and causing the thermostat to stay engaged longer or more often.
Tom

Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 6:55 pm
by MtnDon
Rather than a rheostat consider an electronic PWM controller. Lots on ebay. Here's one I have used on several things. And another. 2 to 3 weeks from China.

A rheostat turns power into heat when it limits power output to the device. A PWM controller has very low loss. As it operates it turns the power flow off and on, thousands of times a second. If the frequency is high enough they are silent. The ones I linked to are high frequency. I've used them on DC ceilking fans, a water pump (not the one in the trailer) and a small CPU fan I use in the Truckfridge to circulate air inside the fridge.

Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 7:09 pm
by lrrowe
Socal Tom wrote:
lrrowe wrote:Same here. My pump is lower then the hot water tank exit. No priming needed. I used it this week for a 4 day outing at VA Beach with a TearJerker event and it worked perfectly. I turned the heat down to 64 for the night and all was great.
My next modification will be to put a rheostat on the fan to slow it down and maybe one on the pump so the hot water will flow through the heater more slowly thus maybe reducing the propane used.

Also my air flow has slowed down. Seems like I broke one of the fan blades last fall and had to purposely break off one on the opposing side to balance things out. That for sure reduced the air flow.


The best way to slow the water flow would be a needle valve upstream of the pump. This will also reduce the power used by the pump. On the other hand a rheostat will probably increase the power used.
FWIW, slowing the water flow is unlikely going to reduce the propane load. The propane is being used because you have taken BTUs out of the water, and the amount of BTUs needed won't change based on the flow rate of the pump. However, if you lower the speed of the pump, then you might reduce the rate at which the BTUs are removed ( the BTU transfer is most effeient when the air temp and water temp are farthest apart) and potentially use more propane, since you would spend more time sending cold water into the tank, and causing the thermostat to stay engaged longer or more often.
Tom


Interesting. I think you are saying that if I run the pump slower, I could remove more of the water's heat and thus send colder water back to the heater. If so, then more propane would be used. If I have this right, the cost of DC current used is far less then propane. Maybe you just talked me into not slowing the pump down.

Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 7:12 pm
by ELM
I'm thinking of using this heater from Jegs http://www.jegs.com/i/JEGS+Performance+ ... 0/10002/-1
I know I could build a heater cheaper but this one looks nice and would be quick.
They do also sell others.
http://www.jegs.com/i/JEGS-Performance- ... oreDetails
http://www.jegs.com/i/JEGS-Performance- ... Id=1697917
http://www.jegs.com/i/JEGS-Performance- ... Id=1697917

Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 7:13 pm
by lrrowe
MtnDon wrote:Rather than a rheostat consider an electronic PWM controller. Lots on ebay. Here's one I have used on several things. And another. 2 to 3 weeks from China.

A rheostat turns power into heat when it limits power output to the device. A PWM controller has very low loss. As it operates it turns the power flow off and on, thousands of times a second. If the frequency is high enough they are silent. The ones I linked to are high frequency. I've used them on DC ceilking fans, a water pump (not the one in the trailer) and a small CPU fan I use in the Truckfridge to circulate air inside the fridge.


Please excuse my layman terms used sometimes. It is like my fingers type faster then my brain works. I said thermostat but I actually meant the PWM type controllers. Actually I forgot I just ordered and received three of them the other week. I will give them a try.

Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 7:54 pm
by Socal Tom
lrrowe wrote:
Socal Tom wrote:
lrrowe wrote:Same here. My pump is lower then the hot water tank exit. No priming needed. I used it this week for a 4 day outing at VA Beach with a TearJerker event and it worked perfectly. I turned the heat down to 64 for the night and all was great.
My next modification will be to put a rheostat on the fan to slow it down and maybe one on the pump so the hot water will flow through the heater more slowly thus maybe reducing the propane used.

Also my air flow has slowed down. Seems like I broke one of the fan blades last fall and had to purposely break off one on the opposing side to balance things out. That for sure reduced the air flow.


The best way to slow the water flow would be a needle valve upstream of the pump. This will also reduce the power used by the pump. On the other hand a rheostat will probably increase the power used.
FWIW, slowing the water flow is unlikely going to reduce the propane load. The propane is being used because you have taken BTUs out of the water, and the amount of BTUs needed won't change based on the flow rate of the pump. However, if you lower the speed of the pump, then you might reduce the rate at which the BTUs are removed ( the BTU transfer is most effeient when the air temp and water temp are farthest apart) and potentially use more propane, since you would spend more time sending cold water into the tank, and causing the thermostat to stay engaged longer or more often.
Tom


Interesting. I think you are saying that if I run the pump slower, I could remove more of the water's heat and thus send colder water back to the heater. If so, then more propane would be used. If I have this right, the cost of DC current used is far less then propane. Maybe you just talked me into not slowing the pump down.


No, but yes :roll: Here is what i "think" would happen, I'm going to make up numbers because it will be easier to explain so bear with me.
Let say that if 1 gallon of water drops 1 degree that is 1 Tom Thermal unit ( like a BTU but with gray hair).
So it it takes 300 TTU/hr to warm your cabin, then either you need 300 gallon/ degrees to keep it warm.
if you have 120 degree water going into the HC ( Heater core) at 2 gallons per minute and it drops 50 degrees then you transfer 100 TTU per minute so you have to run the pump for 3 minutes per hour to warm the cabin. ( This assumes that the water heater can produce a consistent 120 degree water)
Now if you cut the water flow in half, then you pump 1 gallon per minute, but you only get an 80 degree drop in the water so now it takes closer to 4 minutes to warm the cabin. ( and I assume now that the water heater has to run for 4 minutes instead of 3).
Now if the water heater has to run 15 minutes for every 3 minutes the pump runs, then you are still better off with it at full speed because the greater the difference between the water and the air, the more efficient the heat transfer ( This is why cars don't over heat when its freezing outside, but they do when its a 100 degree day)

Re: Heating using the hot water tank.

PostPosted: Thu Apr 21, 2016 8:06 pm
by Socal Tom
lrrowe wrote:
MtnDon wrote:Rather than a rheostat consider an electronic PWM controller. Lots on ebay. Here's one I have used on several things. And another. 2 to 3 weeks from China.

A rheostat turns power into heat when it limits power output to the device. A PWM controller has very low loss. As it operates it turns the power flow off and on, thousands of times a second. If the frequency is high enough they are silent. The ones I linked to are high frequency. I've used them on DC ceilking fans, a water pump (not the one in the trailer) and a small CPU fan I use in the Truckfridge to circulate air inside the fridge.


Please excuse my layman terms used sometimes. It is like my fingers type faster then my brain works. I said thermostat but I actually meant the PWM type controllers. Actually I forgot I just ordered and received three of them the other week. I will give them a try.


PWM is much more effient that a rheostat, but the needle valve might(?) still be better. If you remember your high school physics days, work = mass x distance. If you cut the flow of water in 1/2 then the pump does half the work, even if you have increased the pressure in front of the pump. Using a PWM might accomplish the same savings though, since the math is the same.

And this reminds me of a story I'll share ( those of you who don't like stories can skip this part)
So I'm in college, (picture a scrawny college kid with glasses), and I'm working on campus at the Central plant ( Picture a building with Boilers, 50 HP pumps and a dozen retired Navy Chiefs/ Machinist mates). So one of the pumps is overheating and drawing too much power ( they monitor everything!), and so they are going to close the output valve a bit to lower the power draw of the pump. Of course the scrawny college kid tells them that won't work. ( His 20 or so years in school making think he knows more than their 30+ years messing with pumps and electricty) so we ( I mean they) :roll: go down to the pump and hook up an ammeter to the pump motor. The close down the valve on the pump and the damn amperage goes down , and the scrawny kid learned a lesson he hasn't forgotten ( I wish they had done that in physics class).

Re: Heating using the hot water tank.

PostPosted: Fri Apr 22, 2016 5:57 pm
by lrrowe
Thanks Tom. I hate to say it, but I am a great example of the " if you do not use it, you lose it" fable. I took HS and college physics and remember little of it. Thank you and the others who bring back memories.

Re: Heating using the hot water tank.

PostPosted: Tue May 03, 2016 2:39 pm
by Shadow Catcher
It works :D
I de-winterized the trailer and we tested the heater today making sure none of the new plumbing leaked and all the bits and pieces played well together.
I still have to do some some permanent wiring and make things look a bit less like a well, mess.
The double quick disconnects work with only a couple of drops of water despite being full pressure.
141350
Needs to be neatened up and re do hoses and wiring.
141348
Plumbing and wiring are just a bit crowded
141349

Sam (RV Doctor) who did the plumbing was very surprised it actually worked and called one of his workers over to witness. :applause:

Re: Heating using the hot water tank.

PostPosted: Tue May 03, 2016 3:13 pm
by lrrowe
Great. I think we have the same type pump and I like the portability (to a degree) of your heater box. Mine worked great at the TearJerkers event at VA Beach the other week. We had to turn it down to be comfortable.

Edit: Do we (You, MtnDon and I) all get Merit Badges for our project?