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Author Topic: Space Heating from Engine Heat  (Read 523 times)

veggie

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Space Heating from Engine Heat
« 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.

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
« Last Edit: October 31, 2019, 11:36:15 PM by veggie »
- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw

glort

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Re: Space Heating from Engine Heat
« Reply #1 on: November 01, 2019, 05:19:26 AM »
yes
« Last Edit: November 02, 2019, 01:51:03 AM by glort »

mike90045

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Re: Space Heating from Engine Heat
« Reply #2 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 ?

snowman18

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Re: Space Heating from Engine Heat
« Reply #3 on: November 01, 2019, 08:30:18 AM »
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

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

veggie

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Re: Space Heating from Engine Heat
« Reply #4 on: November 01, 2019, 01:43:17 PM »
Are you using a thermostat in the engine coolant to keep the engine hot, about 190F or just straight thermosiphoning ?

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)


« Last Edit: November 01, 2019, 11:00:45 PM by veggie »
- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw

saba

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Re: Space Heating from Engine Heat
« Reply #5 on: November 02, 2019, 01:44:05 AM »
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


   

broncodriver99

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Re: Space Heating from Engine Heat
« Reply #6 on: November 02, 2019, 02:53:57 PM »
For those on the Metric system 190 F = ~88 C and 3412 BTU = 1 kw.

broncodriver99

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Re: Space Heating from Engine Heat
« Reply #7 on: November 02, 2019, 03:50:26 PM »
Stepping up your storage temp from 160 F to 180 F would net you another 8300 btu. Obviously though the hotter you go the more care you need to take with safety mechanisms. At a minimum you will need an expansion tank of probably a couple gallon capacity to handle the expansion of the fluid since you will be swinging the temperature around 100 degrees. If you figure the total water volume in your system you can calculate how big of an expansion tank you would need. A PT valve would be necessary as well.

As for controlling the heat output to help bank the energy yes you could cycle the pump and fan. There are also 3 way bypass valves that can be set up various ways to help control how much energy you are using. What kind of space temp are you trying to maintain? Above freezing or more livable temps? With a 3 way valve you can set it up to sense the supply or return fluid temp of the fan coil. You could set it for say 70 degrees and it will mix the fluid supply to the unit heater to maintain that temperature. As your overall fluid temperature drops the valve would bypass less and less using more "hot" water to try to maintain whatever fluid temperature you are trying to maintain for the unit heater. The oversized unit heater will definitely help you when trying to extract heat at the lower temps but I would suggest slowing the fan down. Varying the fan speed would be another method of controlling how much energy you spend.

The bypass valve would help level out the usage so you could just set up a simple timer program to cycle the pump and fan coil without needing to process temperatures with a microprocessor or just let the system run on the thermostat. I would use a simple line voltage space thermostat to control the pump and unit heater and then let the bypass valve manage the fluid. That is the simplest method I can think of. I do think that the air flow of that unit heater is going to be a challenge.

veggie

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Re: Space Heating from Engine Heat
« Reply #8 on: November 02, 2019, 05:37:36 PM »
Thanks Bronco, Good suggestions.
The unit heater actually has a 3 speed fan. It would not be difficult to switch speeds based on fluid temperature.
There is one power wire for each of the 3 speeds. Whichever wire has power produces a different speed.

I will also check into the bypass valves. I was already considering one for the H20 solar panel heat dump loop.

Yes. Maybe I can push the temp up a little and gain some more energy storage.
I do have a 3 gallon expansion tank kicking around.
Once the evacuated tubes are on-line I can push even more heat into the system.
« Last Edit: November 02, 2019, 05:47:13 PM by veggie »
- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw

veggie

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Re: Space Heating from Engine Heat
« Reply #9 on: November 02, 2019, 05:56:13 PM »
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

Thanks Bernard,
Yes, my Lister should be able to heat the tank from 60f to 170f in approx. 4.5 hours when using heat from the cooling system as well as power
from the generator (heating element). My concern was more to do with how to budget the use of the tank water heat over a 12 hour period (night).
I am not collecting exhaust heat because I have not yet found an exhaust gas heat exchanger that it A] Efficient enough and, B] Practical to clean.
So I'm pushing the exhaust outdoors in to a silencer box similar to what you built.



- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw