CHP Unit: "The Generator"

[Ronmar]

Intro:  My name is Ron Marlett. I live in the Pacific Northwest. I am a retired Chief Electronics Technician, USCG.  I have been wrenching on things that turn fuel into heat and noise since I could walk.

Operational Philosophy:  This unit was developed initially to provide electrical power to operate a pellet stove and power my house when other power was unavailable.  It's intended use is for less than 12 hours a day.  Since this is such a small load, it quickly grew to allow the powering of the basic lighting and appliance loads, as well as powering the well pump.  These needs were quite easily met with the then readily available 6HP slow speed engine, commonly referred to as a Listeroid. I also favored this engine due to it's potential for long service life, and it's low fuel consumption.  It is also not unpleasant to be around like many generators I have worked with over the years.  Early on in my design, I was a little frustrated that the only thing I could not provide for my family's comfort was hot water.  The electric water heater load is just too great, without going to a much larger generator.  A little further research showed me that it was quite easy and very economical to recover the waste heat from this liquid cooled engine.  So before completion, the plan was shifted from simple backup electricity generation to that of Combined Heat and Power generation.. 

Bill of Materials:  2004 vintage pre-ban 6HP/Single cylinder slow speed engine based on the Lister CS series liquid cooled engine design, $1200. "ST" type 5KW, 1800RPM/4Pole harmonically excited generator head with 8groove serpentine drive pulley, $315.  5X12, 10 plate Brazed Flat plate Heat Exchanger,  $95.  14"X14"X4" fan coil unit, $127. Taco 004 circ pump, $97.  Misc steel for foundation, drive belt and fittings/hardware. $200.  1300# concrete base block was free/recycled.   

Theory of operation:  As stated the original intent of this project was to allow me to power a pellet stove to heat my home during loss of commercial power, as well as maintain reefers and freezers, lights and entertainment/communications.  In that regard, I am sure it is similar to other systems in that it generates 240V(split 120) 60HZ electric power used domestically in the USA and Canada.  The primary engine coolant is a non-toxic propylene glycol type.  The engine cooling system is non-pressurized and for efficiency and reliability, circulates without a pump via thermo-siphon thru a 195F automotive thermostat to the heat exchanger.  The system uses a brazed flat plate heat exchanger in place of a traditional radiator to carry away the engines cooling system heat.  The secondary loop operates at domestic water pressure of around 50 PSI.  From the secondary loop of the heat exchanger, the heat is thermostatically regulated to 120F and directed to the top of the domestic hot water tank The water returning to the heat exchanger is from the bottom of the domestic tank and returns via a fan coil unit that dissipates any heat from the water above the ambient air temperature.  This insures that the water temperature returning to the heat exchanger is adequate to meet the cooling needs of the engine.  Because of the modular construction I chose, this fan coil unit can either be connected inside the dwelling if the season warrants the heat being put into the dwelling, or outside if no heat is required inside the dwelling.  This probably differs from other CHP systems in that only enough hot water(50 gallons) is stored in my system to meet basic domestic needs.  Once the tank is full of hot water and the tank outlet temp starts to rise, the fan coil starts to dissipate heat.
 
Development: Stage 1(complete) engine and foundation prep.  These engines are not the highest quality and require some setup skill to prep them for long term service.  The mounting and foundations must also be prepared.  I balanced the engine for the lowest perceived vibration and then to further dampen any vibrations I mounted it to a #1300 block of concrete, that rests on a ½" rubber pad.  This installation method has so far provided very good service.

Stage 2(complete): Cooling system and power generation.  Initially, I had planned for a radiator, but early on I shifted this plan to a water to water heat exchanger.  Due to cost I had initially planned on building this myself, then I discovered the wonderful brazed flat plate heatex.  This jewel met all my needs and allowed me to continue to use thermo-siphon.  It also greatly simplified installation as I no longer had to plan for ducting large quantities of cooling air to a radiator.  The generator had almost no issues, and was bolted in place and connected to the engine via large serpentine automotive belt.  This drive is very smooth and the connection of the generator allowed me to break-in the new engine and test the cooling system under load.  I configured the heat exchanger secondary to put heat into a 25 gallon drum for testing purposes. 

Stage 3(complete):  Installation and connection to house service panel.  This stage went well considering the #2300 weight of the finished generator.  It moved quite easily on rollers pushed by hand or with levers.  The power connection was done using a interlocked back-feed circuit breaker to provide the generator power to my main panel for distribution.

Stage 4(functionally in progress): Permanent connection of heat exchanger to domestic hot water storage tank. This posed some problems as my generator room is an adjacent cinder block structure.  As a temporary solution, I have 2 dedicated hoses that I can connect to the hot water heater drain and a hot water tap point in my domestic system to harvest the heat when the generator is on line.  I place the hoses that are run outside into precut foam sandwich blocks for insulation.  This is slightly cumbersome to setup, so I will be adding 2 dedicated insulated faucets for this purpose to ease connections later this summer.  This will drastically reduce setup time and shorten the outside hose runs that require insulation..  As this system is only used for backup, this is probably as permanent as I will make it.  We have new house plans for another area of the property, and this structure that we currently occupy will make a wonderful barn.  The new house will have the generator heat recovery incorporated as part of the plumbing/heating design.

Stage 5(research, design and planning phase): Exhaust heat recovery.  I am currently researching two different design ideas to recover exhaust heat from a relatively low power output diesel.  One involves a relatively traditional approach, but with a twist that makes it VERY easy to clean and maintain.  The second will be nearly self cleaning, and provide some exhaust scrubbing.  I should have a prototype of the second design running this summer.   
I call it "The Generator"  I know, not very original, but consider the source...

[Ronmar]

As soon as I get something working, I will:)

[Crumpite]

I'm interested in how you hooked up the auto thermostat into your thermosyphon cooling system.

Sounds like a nice setup, somewhat like mine.
Crumpite

[Ronmar]

I'm interested in how you hooked up the auto thermostat into your thermosyphon cooling system.

Sounds like a nice setup, somewhat like mine.
Crumpite

Crumpite, I went over how my thermostats are installed in this thread  over on the lister engine forum.
http://listerengine.com/smf/index.php?topic=5346.15

Jens, the second method I am going to experiment with is the direct contact type we have discussed before.  The orher is a personal twist on a proven heatex design. Beyond that you will have to be patient.  I don't mind risking a little of my own time in persuing a concept, but I won't waste any one elses untill I have some solid go/nogo info...