Post by keelz on Feb 9, 2009 19:18:06 GMT 10
ok after much kickin' and naggin' LOL here is a separate thread to kick off discussion and share the good and bad about improving ventilation and operation of the absorption type fridges found in our classic 70's vans.
Bear in mind that a lot of our older fridgers are only N or SN rated and can really only manage 25 degrees below ambient. With some basic venting improvements you can improve performance of the fridge during warmer weather. Unless you have a 'T' rated newer model fridge (Rated for up to 43deg ambient), chances are you will find the results of a digital thermometer or data logger very interesting if you check out your fridge on a hot day.
Note: If taking measurements, make sure you place the probe in a cup of cool water and let the fridge cool that water for a few hours and the measurement of the actual temp will be much more stable compared to air temp measurements inside the cabinet which fluctuate as you open and close the fridge!
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Currently the existing louvres in the van wall and removable panel have just not been allowing enough airflow, it comes down to cross sectional area/open airflow and these things were just not cutting it to allow the fridge to breath adequately. The top vent was also badly configured from the time the van was built, sealed off with flymesh full of dust, etc. On a hot day the fridge has been suffering as a result and performance hampered.
After having the fridge re-built earlier this year i have fitted 12 volt fans on the back of the fridge that are switched via a thermostat on the coils as the weather warms up and the fridge cranks up the heat to keep up, they automatically kick in, or I can manually overide.
Next had to improve the venting to create a better draught behind the fridge.
In with the new Dometic vents. I always hate having to cut more holes in the van walls and this was a tricky location to make watertight but I think the end result and improved fridge performance will be worth it. Pic with the upper vent now in, I couldn't decide on using the 4 inch grinder, the jigsaw or my recipro saw for this job. I ended up running with the 4inch with a fine/narrow aluminium cutting blade. Worked a charm with 4 rounded holes in each corner done by the drill bit. This allowed me to cut the outside face first without trying to have a large blade punching in and out of the wall cavity and hitting inside panelling with the other two options........
This vent is taller above the top of the fridge and required modification of the venting setup internally so i can install a metal heat shield under the existing plastic splay duct.
So i started knocking it up
test fit and view of the vent internally, much bigger opening than the old setup. The original setup had a small rectangular cut-out in the timber panelling, to allow the hot air to vent up the wall cavity and out the louvres. Problem was the hot air was getting trapped inside the wall cavity and just wasn't escaping.... This new top vent also has allowed me to fabricate a new flue extension to the top of the gas flue exhaust pipe, now fully ducted externally via the vent kit and t-piece section. Less heat in the cabinet area, more heat going outside
another test fit - with the old plastic duct on top.
side view - much higher now due to increased wall opening height.
running much cooler now with a test run for a cpl of hours with things sitting loosely in position
after a couple of simulated sundown 'beer runs' - door opens door shuts.... is now pulling better temps, have also put the fridgemate battery fan inside for a test run - it seems to help the cabinet temperature pull back down to temp a lot faster by helping with a bit of air movement, so that little fan is coming on our next trip
the fridgemate running internally
Finally i am starting to get some nice frosty fins with it cranking a few deg's cooler just wait till i get this thing loaded up lotsa cold stuff
Get onto Google and start looking up three way fridges, venting, 12volt fans, etc. There is hundreds of pages of information useful for assisting.
Here are some starter references for the venting requirements.
www.caravanandmotorhomebooks.com/articles/fridges_two.htm
www.fridge-and-solar.net/fridge_vent.htm
www.rvmobile.com
The original vent design of the Viscount setup was a good attempt, but after doing some reading i came to the conclusion that it was less than satisfactory to get the best results out of the fridge.
I also came across a website with all the Dometic manuals for all the fridge models, very handy if you have bought an old classic without any manuals....Yee haa
www.dometicmanuals.com:8080/dometic/masterdometic.nsf?Opendatabase
At present i have two 12volt fans located on the back. I'm experimenting with the use of 1 and 2 fans individual and combined, with slightly different fan capacities. The thermostat is a 12volt normally open thermostat switch.
When the middle coils on rear of fridge heat up over about 70 deg the fans come on automatically. I have a bypass wire fitted to the switch on top of the fridge near the vent that allows me to override and switch the fans on earlier if we are expecting a stinkin' hot day. The fans at the back have resulted in reducing the fridge temp on average by about 3-4 degrees on an normal day. It is amazing how much just a bit of airflow up behind the fridge helps. I used to hold my hand near the old ally wall vents and didn't feel much air movement (even with the fan fitted).
Now i hold my hand in front of the top Dometic vent and can feel a steady flow of warm air
the vent kit came from caravansplus with the couple of extension pieces as shown on their site. Due to the height of my fridge, the black extension pieces were too short and their diameter was too small for the existing flue discharge diameter on the fridge. I have used the top aluminium piece and the metal t-section that came with the kit. The fridge used to have an aluminium flue with a small vent hole in the top. I removed this and scrounged around the garage. I found a length of old Electrolux vacuum cleaner aluminium hose pipe in matching diameter and wall thickness! Perfect - I chopped a section down and have very crudely connected it together for now.
The heat that comes out the top plastic vent dissipates pretty well, the passing breeze external helps remove the exhaust gases quickly. The plastic is the same stuff that the gas hot water heater louvre is made out of, it seems to cope ok. The only downside is that after test running the gas i reckon that i got a couple of flame-outs.....but this only happened once during extremely windy weather. The best thing is it's helping to get rid of the nasties outside into the atmosphere, not sitting inside your van.
Here is the fan arrangment with the rear linings/baffle covers removed....the fans you need are the ones out of the old computer power supplies. Find some old computers and strip the fans out of the power supplies. Usually they have 2-3 wires, just go for the red and black. I've found that one fan is satisfactory. I've got two because one is wired full time to the tow vehicle 12v feed to the 12v element on the fridge and the second fan is just wired to a plug pack transformer that i've got in the cupboard under the sink.
Use a bit of 25 x 25 aluminium angle, notch out a section for the fan's airflow path, drill a few screw holes and there you go!
The small fans from the motherboard chips might be a bit small to get the required air movement. I reckon they would be ideal however to use inside the fridge cabinet to circulate cool air. Some of those smaller fans might run off 3v? or so.
I've seen some guys who also use a power supply fan inside the fridge cabinet and just run it off the same 12v circuit by sneaking some wires into the cabinet through the holes that the thermostat wires feed through into the cabinet instead of purchasing/using a Fridgemate fan...
New matching lower vent (old louvre sections blanked off to help create draft path starting down low at bottom vent, up over absorber, coils and top coiling fins and out through top vent)
Then back inside the van. Fabricating new heat deflector out of sheety ally to fit the new upper vent box/enclosure.
test fit with plastic cover back on top for aesthetics and it has foam gasket strips installed all over it to seal out air and insect movement into van.
The movement of hot air out the top vent is much more noticeable now since the installation of the new vent kit, i could never feel much air movement coming out of the old louvres due to the bad flow path inside the cavity wall.
Ok this is just a starting point and may assist others reviewing the venting of their fridges. Feel free to add to this and hope it helps others.
Cheers
Keelz
Bear in mind that a lot of our older fridgers are only N or SN rated and can really only manage 25 degrees below ambient. With some basic venting improvements you can improve performance of the fridge during warmer weather. Unless you have a 'T' rated newer model fridge (Rated for up to 43deg ambient), chances are you will find the results of a digital thermometer or data logger very interesting if you check out your fridge on a hot day.
Note: If taking measurements, make sure you place the probe in a cup of cool water and let the fridge cool that water for a few hours and the measurement of the actual temp will be much more stable compared to air temp measurements inside the cabinet which fluctuate as you open and close the fridge!
-----------------------------------------------------------------
Currently the existing louvres in the van wall and removable panel have just not been allowing enough airflow, it comes down to cross sectional area/open airflow and these things were just not cutting it to allow the fridge to breath adequately. The top vent was also badly configured from the time the van was built, sealed off with flymesh full of dust, etc. On a hot day the fridge has been suffering as a result and performance hampered.
After having the fridge re-built earlier this year i have fitted 12 volt fans on the back of the fridge that are switched via a thermostat on the coils as the weather warms up and the fridge cranks up the heat to keep up, they automatically kick in, or I can manually overide.
Next had to improve the venting to create a better draught behind the fridge.
In with the new Dometic vents. I always hate having to cut more holes in the van walls and this was a tricky location to make watertight but I think the end result and improved fridge performance will be worth it. Pic with the upper vent now in, I couldn't decide on using the 4 inch grinder, the jigsaw or my recipro saw for this job. I ended up running with the 4inch with a fine/narrow aluminium cutting blade. Worked a charm with 4 rounded holes in each corner done by the drill bit. This allowed me to cut the outside face first without trying to have a large blade punching in and out of the wall cavity and hitting inside panelling with the other two options........
This vent is taller above the top of the fridge and required modification of the venting setup internally so i can install a metal heat shield under the existing plastic splay duct.
So i started knocking it up
test fit and view of the vent internally, much bigger opening than the old setup. The original setup had a small rectangular cut-out in the timber panelling, to allow the hot air to vent up the wall cavity and out the louvres. Problem was the hot air was getting trapped inside the wall cavity and just wasn't escaping.... This new top vent also has allowed me to fabricate a new flue extension to the top of the gas flue exhaust pipe, now fully ducted externally via the vent kit and t-piece section. Less heat in the cabinet area, more heat going outside
another test fit - with the old plastic duct on top.
side view - much higher now due to increased wall opening height.
running much cooler now with a test run for a cpl of hours with things sitting loosely in position
after a couple of simulated sundown 'beer runs' - door opens door shuts.... is now pulling better temps, have also put the fridgemate battery fan inside for a test run - it seems to help the cabinet temperature pull back down to temp a lot faster by helping with a bit of air movement, so that little fan is coming on our next trip
the fridgemate running internally
Finally i am starting to get some nice frosty fins with it cranking a few deg's cooler just wait till i get this thing loaded up lotsa cold stuff
Get onto Google and start looking up three way fridges, venting, 12volt fans, etc. There is hundreds of pages of information useful for assisting.
Here are some starter references for the venting requirements.
www.caravanandmotorhomebooks.com/articles/fridges_two.htm
www.fridge-and-solar.net/fridge_vent.htm
www.rvmobile.com
The original vent design of the Viscount setup was a good attempt, but after doing some reading i came to the conclusion that it was less than satisfactory to get the best results out of the fridge.
I also came across a website with all the Dometic manuals for all the fridge models, very handy if you have bought an old classic without any manuals....Yee haa
www.dometicmanuals.com:8080/dometic/masterdometic.nsf?Opendatabase
At present i have two 12volt fans located on the back. I'm experimenting with the use of 1 and 2 fans individual and combined, with slightly different fan capacities. The thermostat is a 12volt normally open thermostat switch.
When the middle coils on rear of fridge heat up over about 70 deg the fans come on automatically. I have a bypass wire fitted to the switch on top of the fridge near the vent that allows me to override and switch the fans on earlier if we are expecting a stinkin' hot day. The fans at the back have resulted in reducing the fridge temp on average by about 3-4 degrees on an normal day. It is amazing how much just a bit of airflow up behind the fridge helps. I used to hold my hand near the old ally wall vents and didn't feel much air movement (even with the fan fitted).
Now i hold my hand in front of the top Dometic vent and can feel a steady flow of warm air
the vent kit came from caravansplus with the couple of extension pieces as shown on their site. Due to the height of my fridge, the black extension pieces were too short and their diameter was too small for the existing flue discharge diameter on the fridge. I have used the top aluminium piece and the metal t-section that came with the kit. The fridge used to have an aluminium flue with a small vent hole in the top. I removed this and scrounged around the garage. I found a length of old Electrolux vacuum cleaner aluminium hose pipe in matching diameter and wall thickness! Perfect - I chopped a section down and have very crudely connected it together for now.
The heat that comes out the top plastic vent dissipates pretty well, the passing breeze external helps remove the exhaust gases quickly. The plastic is the same stuff that the gas hot water heater louvre is made out of, it seems to cope ok. The only downside is that after test running the gas i reckon that i got a couple of flame-outs.....but this only happened once during extremely windy weather. The best thing is it's helping to get rid of the nasties outside into the atmosphere, not sitting inside your van.
Here is the fan arrangment with the rear linings/baffle covers removed....the fans you need are the ones out of the old computer power supplies. Find some old computers and strip the fans out of the power supplies. Usually they have 2-3 wires, just go for the red and black. I've found that one fan is satisfactory. I've got two because one is wired full time to the tow vehicle 12v feed to the 12v element on the fridge and the second fan is just wired to a plug pack transformer that i've got in the cupboard under the sink.
Use a bit of 25 x 25 aluminium angle, notch out a section for the fan's airflow path, drill a few screw holes and there you go!
The small fans from the motherboard chips might be a bit small to get the required air movement. I reckon they would be ideal however to use inside the fridge cabinet to circulate cool air. Some of those smaller fans might run off 3v? or so.
I've seen some guys who also use a power supply fan inside the fridge cabinet and just run it off the same 12v circuit by sneaking some wires into the cabinet through the holes that the thermostat wires feed through into the cabinet instead of purchasing/using a Fridgemate fan...
New matching lower vent (old louvre sections blanked off to help create draft path starting down low at bottom vent, up over absorber, coils and top coiling fins and out through top vent)
Then back inside the van. Fabricating new heat deflector out of sheety ally to fit the new upper vent box/enclosure.
test fit with plastic cover back on top for aesthetics and it has foam gasket strips installed all over it to seal out air and insect movement into van.
The movement of hot air out the top vent is much more noticeable now since the installation of the new vent kit, i could never feel much air movement coming out of the old louvres due to the bad flow path inside the cavity wall.
Ok this is just a starting point and may assist others reviewing the venting of their fridges. Feel free to add to this and hope it helps others.
Cheers
Keelz
I see what you mean so now I have a handle on it. Hope I don't forget by the time I get to the van ;D