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Space Heating from Engine Heat

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veggie:
I have calculated that my 50 gallon solar storage tank can supply my garage with 12 hrs of heat between 160 Degf and 50 Degf if I heat it to the upper value and then draw 3500 btu/hr in the form of a fan/radiator until the lower value is reached. To help heat my garage space.

I can charge the tank to 160f by running the Listeroid for 4 hrs and transfering the coolant heat and electrical heat (via an electric heating element) to the tank fluid.

I have a fan/coil capable of 18500 btu's output which can be piped to the tank and be energized to blow heat into the space when the tank liquid reaches 160f.

Problem:
When the fan/coil is energized it will exchange far more heat (Btu's) when the water temperature is at 160f than it will when the water temp falls to, say 65f.
So I will get most of my heat transfer taking place in the first few hours of the cycle and little transfer later in the cycle becasue of the lower differential temps across the radiator as the water loses heat.
If I can pull a constant 3500 btu's from the tank, it should last 11 - 12 hours through the night.

What do you guys think of this solution....

Cycle the Fan/Coil based on tank temperature so excess heat is not expelled at the start of the cycle.
Basically cycling the fan (and circ pump) to control the release of heat over time.

As and example...
(Just for illustration, I have not calculated these values yet.)

======= FAN/COIL CYCLING==========
Tank Temp    Cycle time (ON-OFF) Minutes
==================================
160             5 - 10 Short heating cycle
150             6 - 10
140             7 - 10
130             8 - 10
120             9 - 10
110             10 - 9
100             11 - 8
90              12 - 7
80              13 - 6
70              14 - 5
60              15 - 3
50              16 - 0 Long heating cycle

Does this approach make sense?
A simple Arduino program with a motor relay could run the heater fan and circ pump.

Some of you guys that are more familiar with heating and cooling systems may have an opinion as to whether I'm on the right track.?
I would use this as an initial system to prove the garage CHP model.
Later I could make the controls more intelligent by having the microcontroller measure the change in tank temperature over time (BTU's used and BTU's remaining) and dynamically adjust the fan cycle time to budget the heat over a 12 hour period.

And is an tank target temperature of 160f realistic? or should I take it higher and store more heat?

cheers,
veggie

mike90045:
Are you using a thermostat in the engine coolant to keep the engine hot, about 190F or just straight thermosiphoning ?

snowman18:

--- Quote from: veggie on October 31, 2019, 11:30:34 PM ---I have calculated that my 50 gallon solar storage tank can supply my garage with 12 hrs of heat between 160 Degf and 50 Degf if I heat it to the upper value and then draw 3500 btu/hr in the form of a fan/radiator until the lower value is reached. To help heat my garage space.

cheers,
veggie

--- End quote ---

Load your50 gallon water tank with soapstone for better heat retention.

veggie:

--- Quote from: mike90045 on November 01, 2019, 05:49:10 AM ---Are you using a thermostat in the engine coolant to keep the engine hot, about 190F or just straight thermosiphoning ?

--- End quote ---

The engine has a 190f thermostat and the water exiting the engine will run into a coil loop inside the solar tank.
After exiting the tank there is a small radiator heat dump which activates if the return water is too hot.

The tank is a well insulated solar hot water collector with dual internal heat exchange coils and a backup heating element.

My main reason for doing this project is twofold.
1] I have all the components collecting dust and want to put them to use. This will offset the cost of the existing heater when the roid is running on WVO. I can learn a lot about hydronic systems at the same time.

2]Greenhouse. Once the system proves itself the fan/coil heater will be moved to the greenhouse on the outside of the garage wall.
My experiments with an electric heater this autumn showed that this heat will be enough to extend my growing season by 1.5 to 2 months on either end of summer by keeping the space warm through the night. That part has been proven the past several growing seasons.

3] This system can be expanded with a second tank once I get my 2 evacuated tube collectors mounted and producing heat.
    The system is totally scale-able.

Back to my original question, does the logic seem sound for my method of stretching the heat over a 12 hour period?
(a question perhaps more suited to the Micro-Cogen forum but nobody looks there anymore)

saba:
To be honest I don't get the question completely I am lost with fahrenheit en BTU's.

A lister 6-1 running 3 kw load, has maybe 30% efficiency(probleby less) the rest is heat losses, exhaust most and cooling water. so 7kw of heat.

There is a formula Q= m*c*deltaT  m is mass the amount of liters c is constant of water times the temp difference. Just google it.

You can roughly calculate how many hours it takes to heat up a boiler.

I used a 800 liter boiler and in mild weather say 10 degr celsius, I produced more then I used so had to stop the lister.

hope it helps

Bernhard


   

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