Thanks for the extra info. I remembered the fact that the A/C unit was operator-adjustable by AMP load. Keeping an eye on this one....
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RV10 air conditioning
- Thread starter 50Pesos
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Thanks for the extra info. I remembered the fact that the A/C unit was operator-adjustable by AMP load. Keeping an eye on this one....
Oh! I forgot to mention he said his shop is available for an hourly fee if anyone wants to spearhead the install for those of us farther away.
He is pretty busy at the moment with various projects but said he would include the link for the alternator in an update email. Sounded like it was an automotive alternator but he has been pretty impressed with its performance and size with good reviews. I was shocked at the numbers myself and feel you on the suspense!
This might be a long couple of weeks haha.Here some of the basic AC physics / math:
Assuming an outside temp of 105F gives you 170 psi and an enthalpy of 48 BTU/lb.
You then expand the coolant which gives you 15F and 104 BTU/lb.
You then compress it back up to 170 psi which gives you 130F into the cooler and it now has 120 BTU/lb.
To get 20,000 BTU cooling you need to boil 357 lb/h. Your compressor therefore needs to do 5714 BTU/h of work (to get the enthalpy raised from 104 to 120) which is 1.7 kW. At 12V, that is 140A.
This assumes a 100% efficient system but it gets you into the ball park, in reality you will need more power, certainly not less.
Now you can play with anything you want but at those assumptions that I put in, you are not going to be lower than 140A at 12V for a 20,000 BTU AC.
Martin R.
San Diego
Assuming an outside temp of 105F gives you 170 psi and an enthalpy of 48 BTU/lb.
You then expand the coolant which gives you 15F and 104 BTU/lb.
You then compress it back up to 170 psi which gives you 130F into the cooler and it now has 120 BTU/lb.
To get 20,000 BTU cooling you need to boil 357 lb/h. Your compressor therefore needs to do 5714 BTU/h of work (to get the enthalpy raised from 104 to 120) which is 1.7 kW. At 12V, that is 140A.
This assumes a 100% efficient system but it gets you into the ball park, in reality you will need more power, certainly not less.
Now you can play with anything you want but at those assumptions that I put in, you are not going to be lower than 140A at 12V for a 20,000 BTU AC.
Martin R.
San Diego
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Your math seems to jive with the recently posted system's claim of 8000 BTU's of cooling, drawing a max of 80 amps. However, your data seems to be based upon a Freon system, where the recently posted unit is using a glycol based system. Not sure how much less efficient Glycol systems are. I am guessing less, otherwise they would be installed everywhere instead of freon.
Larry
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As I understand it, the glycol acts as the heat transfer mechanism from the evaporator for cooling vs airflow only. (think water cooled vs air cooled). Where the Sofie Lite is a traditional type of system (airflow heat transfer only). Both systems using a refrigerant.
Anyways, that's all off the top of the head stuff from Sun N Fun. Looks like there is plenty interest to get something going for the -10 drivers here
.The Sofie system is just a normal AC (like a window unit) with an added chilled water heat exchanger instead of directly blowing the cold air out. As you can see in my example configuration, the temp at the evaporator is some 15F, so they use Glycol to not ice up that remote chilled water loop. The "light" Sofie unit is just a window unit.
In my mind the big Sofie system makes no sense at all for our size planes. We can easily run an air duct from the AC system to where the cold air is needed. No need to add extra weight for the chilled water remote cooling (one extra heat exchanger and the weight of the water). Also with the Sofie system, what are you doing with the condensation water at the front heat exchanger (and along the chilled water hose). Not really then easily portable if you need to somehow collect all that water in the cabin. A fixed installed system will have a pump discharging the water overboard through an installed port.
If you are into an electric AC system, check out the vintage car aftermarket ones. They offer high output alternators, electric compressors and compact evaporator fan units, for example:
https://www.classicretrofit.com/col...conditioning-for-classic-911-dual-condenser-1
Many big cars / SUVs have suitable alternators. There are some 200 to choose from. The question is whether the bearings and the brushes hold up in our airplane environments. If an alternator comes apart up front, it could become expensive. Now PlanePower makes a suitable aircraft one, but it runs $1,800 refurbished, there are no new ones and it is shaft driven, not belt driven.
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High amp alternators are very common for vehicles like the Lincoln Town Car, big SUVs etc.
Here is a search for 200 Amp ones and lots come up:
https://www.oreillyauto.com/search?q=200+amp+alternator
You want the power for the AC to be available at idle / taxi, so you need to go much higher in rating than you need. So a 200 Amp one would probably do fine for our needs and make 100A at idle.
We just don't know what exact changes are made to make alternators aviation grade? Better bearings, stiffer brush springs? It could be that nothing is actually done differently, only the mounting is compatible with Lycoming engines. As long as we can use the B&C remote regulators with OV protection, we should be fine on the electrical side.
