Turbo Cooling, Cabin Heating?

[drPete]

Any opinions from turbo owners on the idea of diverting the cooling fluid in flight into a radiator/fan inside the cockpit for heat?




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[NWade]

Any opinions from turbo owners on the idea of diverting the cooling fluid in flight into a radiator/fan inside the cockpit for heat?

Probably do-able; but you're looking at extra tubing, extra wiring, more valves/fans (i.e. more points of failure and more weight), and more firewall penetrations.

Seat-heaters are likely a simpler, less-costly, and lower-maintenance solution. The only downsides are their power-draw (if you have complex avionics and non-LED navigation/strobe lights) and the fact that they won't heat your feet. :-)

Just my 2 cents, though!

--Noel
Sonex #1339
Aerovee Turbo, Center-stick, Acro-ailerons, Taildragger, Flush Pulled Rivets, MGL Avionics

[Rynoth]

That's... actually quite an interesting idea. The turbo cooling is apparently not necessary during flight, but there also should be no harm in running it during flight (other than the ~2a amp draw.) If you installed the heat exchanger in the cockpit rather than in the engine compartment, you'd be looking at 2 new firewall penetrations for the (longer) coolant hoses and not a whole lot else. On the ground after shutdown, it should cool the turbo as good or even better since the heat exchanger is in a cooler environment than the engine compartment. In the summer, you just don't run it while in the air...

I'm still thinking about my turbo cooling installation since I have a legacy airframe (no room for top-mount), and where to mount the heat exchanger is still very much in question, and the cockpit has not been ruled out as an option.

Hmmm...

[Brett]

I'm trying this radiator as it fits right under my vent. If the vent doesn't work well enough I'm thinking about trying to 3d print a better one.
Hope the pic works..... from my blog wich is a little bit of a sook fest atm unfortunately.

https://2.bp.blogspot.com/-kHTZ6SJ-qG4/ ... 132841.jpg

[kevinh]

Has anyone felt the output air of the radiator? Is it warm enough to make a nice heater? I also have been pondering where to mount it and this idea is interesting.

[Rynoth]

Has anyone felt the output air of the radiator? Is it warm enough to make a nice heater? I also have been pondering where to mount it and this idea is interesting.

More good questions. I'm still accumulating parts for my setup, and I may run some tests in my kitchen using hot water once I have fan/can/pump/heat exchanger & tubing.

The graphs provided by sonex aren't really clear on what the coolant temperature actually is. In flight, they're showing a "bearing" temperature in the ~190 degree range and an "ambient" temperature in the ~110 degree range (is this the coolant temp, or an under-cowling air temp?) I would expect that the coolant temp flowing through the heat exchanger would fall somewhere between these 2 numbers in-flight. For comparison, normal operating coolant temperature in a car, which is used for cabin heating, is around ~200.

The firewall pass-through for the 2 coolant lines to the heat exchanger could use bulkhead fittings like this: https://www.amazon.com/SeaSense-Thru-Bu ... B004XAFICS

[vigilant104]

FWIW, it seems unlikely to me that there will be enough heat in the turbo coolant to significantly warm even the small cabin of the Sonex. The temperature of the coolant (or the temperature of the air from the back side of the radiator) is less significant than the the total number of available BTUs. If we know the coolant temp drop across the radiator and the coolant flow rate we could do the calculation, but I think the results will be disappointing.
Builders of E-AB aircraft with big water-cooled engines have sometimes tried to use the coolant to provide cabin heat ("it works in a car"), but due to effectiveness, weight, and complexity issues, they generally go back to using a heat muff. The heat available from the cooling of the Sonex turbo bearing is going to be >far< less.
There are also safety issues of piping very hot coolant into the small place where the people are located. Not insurmountable, but worthy of consideration.

[Rynoth]

FWIW, it seems unlikely to me that there will be enough heat in the turbo coolant to significantly warm even the small cabin of the Sonex. The temperature of the coolant (or the temperature of the air from the back side of the radiator) is less significant than the the total number of available BTUs.

How many BTU's might be considered margianally effective for our small cockpit? Some brief internet searching suggests that for typical room, 34 BTU per square foot should be sufficient. The footprint of our cabin+baggage is probably less than 25sqft (with a much lower ceiling, no insulation and probably more air leakage than a room), so would 800+ BTU be a reasonable heater?

I'm thinking of performing the following test once I have all my components... put a quart (2lbs) of hot water (maybe 180 degrees) in a thermos to simulate the catch can, run the system for 1 minute, then recheck the temperature of the water. Any reason using the BTU forumula of 1BTU = 1 degree per 1lb of water wouldn't give insight into the BTU capability of the cooling system? Obviously this would not tell us how much the engine compartment/turbo is heating the water on the other end.

[vigilant104]

How many BTU's might be considered margianally effective for our small cockpit? Some brief internet searching suggests that for typical room, 34 BTU per square foot should be sufficient. The footprint of our cabin+baggage is probably less than 25sqft (with a much lower ceiling, no insulation and probably more air leakage than a room), so would 800+ BTU be a reasonable heater?

No, I'm afraid it will be a >lot< more than that.
Here are some rough calculations:
1) If we assume our cabin/fuselage has a total surface area of bout 100 sq feet, that the thin aluminum and plexiglass has a thermal conductivity the same as glass, and that we are heating >no< outside air (i.e. zero ventilation, the radiator works using air from inside the cabin and our cabin is perfectly sealed), and we want a temperature difference of just 30 deg F (e.g outside temperature of 20 degF and we want it to be 50 degF inside), then the heat needed is 3800 BTU/hr.
2) If we make the assumptions above but include 100 CFM of outside "ventilation" (i.e. the air we are running through our heat core/radiator comes from outside the cabin), then we need 7011 BTU/hr. 100 CFM is quite low (less than a typical bathroom fan), I'd bet most Sonexes leak more air into the fuselage than that in flight even with the vents closed.

The above calculations understate the case, maybe by a lot: I've used a regular heat loss calculator ( http://www.loadcalc.net/load.php) that is designed for structures, so there's negligible moving air outside. If instead we are flying and the outside air is flowing over our aluminum skin at 100 kts, it will be losing heat a lot faster. And, as mentioned above, the amount of air moving from outside to inside in flight is probably a lot more than 100 CFM.

As a rough sanity check: A typical candle has a heat output of about 70 watts = 240 BTU/hr. So, three or four of them would provide about 800 BTU/hr. I'm sure we can all agree that burning 4 candles inside a flying Sonex would not provide a noticeable increase in the cabin temps.

Yes, it would be possible to decrease the heat loss considerably by closing off the tailcone, but it's still going to take a lot of heat to make a difference in drafty, uninsulated cockpit.

I'm thinking of performing the following test once I have all my components... put a quart (2lbs) of hot water (maybe 180 degrees) in a thermos to simulate the catch can, run the system for 1 minute, then recheck the temperature of the water. Any reason using the BTU forumula of 1BTU = 1 degree per 1lb of water wouldn't give insight into the BTU capability of the cooling system? Obviously this would not tell us how much the engine compartment/turbo is heating the water on the other end.

Yes, that would give you an idea of how much heat your "core" would be putting out into the cabin. Be sure to keep your units straight: You'll be measuring the BTUs moved by the heating system over the time you are running the rig, and the heat loss numbers above are in BTU/HR. So, if for example, you find the heater core moves 120 BTU in 6 minutes, multiply by 10 to get 1200 BTU/Hr. I think you'll need many gallons of water to get useful information, maybe fill up a 10-20 gallon picnic cooler, let it run for a few minutes to take the lines and radiator up to temp, then start your measurements to learn how much heat is taken out of the water after x minutes. The difference in heat lost through the walls of the picnic cooler vs a thermos bottle won't be a significant source of error over short time periods, both would be swamped by the heat removed through the "radiator."

[GordonTurner]

For compRison, do you know how the numbers look with some typical form of exhaust heat based system?

Gordon