CHP - Engine heat transfer

[veggie]

My lister is already supplying electrical power to the greenhouse heaters in winter.
I want to capture the coolant heat and use it also. My storage is a 50 gallon solar water tank with 2 internal coils.
What limits to storage tank temperature can I expect to reach using the internal exchanger coil in the tank?
I realize that the heat transfer rate drops off as the storage water temperature increases.
The goal to attain a tank water temperature of 175f to 180f before shutting down the engine.
Flow rate is approx 3 gpm through the exchanger/cooling loop.
I'm wondering if the engine will be able to get rid of enough heat when the tank is above160f.
Both the engine loop and the storage tank are open (non-pressurized) systems.

[BruceM]

Hey Veggie,
I think you've got it figured right-  too low delta T with a modest surface area exchange loop.   I'm assuming the engine coolant to solar tank loop is to be pumped or that would be another area where diminished delta T will be a problem.  Pressurizing the engine cooling system and boosting the thermostat comes to mind as one solution in either case, I think.
Bruce

[mike90045]

My thermosiphon tank is an old vehicle gas tank, plumbed up and hung on the wall
It's 15 gallons and is 50/50 antifreeze.  It takes about 60 minutes to warm up to 160F, and as it gets warmer, simply the tank itself, and the open top, start dumping heat faster and faster.  I don't think it would ever boil, but it steams pretty good at 180F  Never seen it above 180F, it just looses heat too fast.

[veggie]

Thanks for your comments gents,
The engine has a 180f thermostat.
As I suspected, as the delta drops, so does the transfer rate, possibly leading to a rapid spike in engine temperature as the delta decreases. A thermal runaway.
The tank is insulated so it can't dump heat as the water temperature climbs.
I have come to the conclusion that a small radiator in the primary (engine) loop will be necessary with a fan that activates when the return water reaches 170 (or something like that).
This way hot water at 180 can leave the engine and travel to the storage tank. If the storage tank can't take all that heat, the rest will be dumped by the small radiator so that the engine can remain cool enough.
I realize that the final 10f accumulated in the tank may take some time due to a low delta-T.

Interesting.... this tank has a 1500 watt electric element also. Once the temperature reaches say 150f, I could activate the heating element and drive the remaining 20 degrees into the tank that way. (Also powered by the listeroid)

System logic:
Once the tank reaches 175f for example, the controller will kill the listeriod and start a fan coil heat exchanger to heat the building space. When the tank temperature drops to 65f, the signal to start the listeroid is sent and the cycle begins again.
Based on my calculated heat loss, in the coldest parts of the winter, the engine would run for 3 hrs .... 4 times per day.

cheers

[BruceM]

An interesting project, Veggie.  Since start/stop will be automated, it will be one step beyond my remote start, auto shutdown 6/1.  Howrah!  Looking forward to seeing your progress on this interesting project, Veggie.  I have the Basic code for my Picaxe 40X2 based controller and remote unit, and schematics for the hand wired circuitry if you'd like it.  I'd use an Arduino if stating over today but in truth the PicAxe was/is well suited.

Best Wishes,
Bruce

[veggie]

BruceM

I'm using the WEMOS version of Arduino. It's an arduino with a ESP8266 WiFi chip on board.
One can code the Wemos/Arduino to publish sensor data to the web using the MQTT protocol for "Internet of things" sensors.
In reverse, I can also send MQTT commands from my cell phone or a laptop to the Arduino in order to shutdown or manually start the machine.

MQTT web sites act as 'brokers" for the data.
My sensors and control boards "publish" data to my account at an MQTT Broker site, and any devise I have can connect to that site and look at the data.
So no more long wires from one device to another.
I do understand that you are not fond of the wireless fog that this may create, but my greenhouse and Lister are far from where I reside.

I also use this process to publish greenhouse data such as indoor & outdoor temperature, nutrient tank temperature, and humidity.
So I can watch the greenhouse conditions from anywhere.
I wrote a watchdog program (Python language) which watches all the sensors at the same time by logging into the broker site and "subscribing" to my sensor data.
If a reading falls outside my programmed parameters the watchdog program sends me a text message or an email.