Geothermal glycol chiller

[stfinder]

I've been reading a lot about geothermal heating/cooling, which can be incredibly energy efficient. Compared to air-source heat pumps which use the air as a heat sink in the cooling process, ground-source heat pumps are typically 3x more efficient and actually deliver more cooling power than the electrical power they consume. In all ground-source heat pump systems there is an heat exchanger that allows the water/antifreeze mixture that circulates through a buried coil to absorb heat from the refrigerant in the heat pump. To me, it seems that the more efficiently the liquid circulating through the buried coil can remove heat from the refrigerant, the more efficient the system would be. And I realized that many homebrewers already use heat exchangers that could efficiently accomplish this task - plate chillers.

I'm wondering if a glycol chiller could be modified to replace the condenser coil with a plate chiller. I don't have any HVAC experience but perhaps someone who has put together their own glycol unit could comment of the feasibility of this prospect. One issue I foresee is the wide inlet on the plate chiller. The compressor does a lot of work to increase the pressure of the refrigerant so that it condenses inside the condenser coil. If there is an increase in the pipe diameter when the refrigerant reaches the plate chiller, this would cause the pressure to drop and it might not condense, making the compressor work harder.

Any thoughts from any of you lovely, more qualified people?

 

[Mr. Vern]

what you are referring to is a water-cooled chiller, yes they exist. 98% of applications use air-cooled condensers but you can easily swap that with a plate heat exchanger for water-cooled. Personally, I am not a big fan of plate heat exchangers because they can clog, but a closed loop glycol system should keep clean and prevent deposits and blockage. you cannot service a plate heat exchanger, they also make Shell & Tube style where you can remove the bonnet and clean the water side without losing refrigerant, but those typically come in larger systems over 1 ton.

You can also buy a plate style chiller that uses a plate heat exchanger instead of the submersed coil that you see on brewing chillers. I have a small plate heat exchanger at home for this purpose but I have not done anything with it yet.

The plate style heat exchanger can be ordered with smaller fittings for refrigerant connection. Line size is not as important here because the refrigerant has already been expanded into a gas, at least thats how it works in my head.

water cooled is more efficient both in cooling and it provides a lower condensing temp to the refrigeration system = less watts.

Homebrew chillers are fractional HP units already, not much of an advantage to be had over the cost of upgrade. The BREWBUILT ICEMASTER MAX4 is a 3/8 HP refrigeration system, probably $0.10 / Hour to operate for my location (12 cents per kwh)

I like how you think, but in reality this system is not a drain on the electrical circuit. if anything making this an evaporative type coil would be ideal but it is not designed that way and will corrode, I have a window AC unit similar size that has a sling on the fan to catch & spray water onto the coil... the coil and electrics would be my concern.

 

[Bobby_M]

Geothermal is only about 25-50% more efficient for cooling but it's only really worth the effort on a full house HVAC that will consume tens of thousands of dollars of energy over its useful life. For running a 5000btu system, it wouldn't be worth the effort to bury a coil.

 

[Broken Crow]

Like Bobby said... diminishing returns. At best you can acheive equilibrium between ground temp and the fluid running through it. As to the plate-chiller.... that's not how refrigeration systems work; as soon as the refrigerant is released into the larger area of a plate chiller, the phase change from liquid>vapor just turns it into another evaporator and the whole unit will overheat.
I've been toying with the idea of using a post-hole digger to drop a couple coils for a closed-loop pumped system for my CFC and steam condenser so as to not waste water, but I'm still working out whether the savings on water would be lost to electric costs and it seems close. A greater energy exchange such as for a glycol chilling might be of use only if your target temperature is equal or higher than your ground temp, and if you're ground temp goes that low, you wouldn't need an HVAC unit, just the glycol filled coils and a pump.

 

[Mr. Vern]

We use plate heat exchangers for both evaporator and condenser, no problem whatsoever. Consider the gas is already expanded when it enters the evaporator and plate selection/design of the evaporator prevents lament flow. Ground temp for condenser use would actually be very nice, we limit water temp at 85F for condenser work but we deal with warmer temps.

To water-cool the condenser you need a good pressure-controlled water regulating valve that monitors head pressure of the refrigerant and adjusts flow to stabilize pressure. If you have constant groundwater temp you could feasibly find the sweet spot with a globe/needle valve and "let it rip"

That said, it is not worth the savings in this size. Someone who does not do refrigerant work could spend upwards to $1,000 to do this and save a couple hundred watts when running. I would equate this upgrade to swapping out 1-2 traditional lights for LED. A 10-20% gain in efficiency on a system that draws 900 watts when running. I dont know the duty cycle of these machines but I would assume 40% or less run time once your storage and/or fermenter have been "pulled down" to normal temp.

Now someone like Coors could benefit from this type of tinkering but a homebrewer not so much.

It is actually my job to do energy calculations on industrial refrigeration packages for rebates. Water-cooled condenser is more efficient, but at this scale it is not very feasible.

OFF TOPIC: We installed some water-cooled condensers at a dairy farm in Cali. We used the refrigeration system to pre-heat water for their various needs. They saved so much gas the energy company came out to investigate! They thought the farm was stealing gas! This was when Cali. mandated the dairy chillers run 2-4 degrees cooler than before, everyone was scrambling to retrofit their system for the new mandate.

 

[Broken Crow]

Thank You Mr. Vern! I've got brain damage that I'm slowly recovering from and I've lost math, 3D cognitive modelling, complexity, etc.. I don't want to hijack the thread, but it seems the OP's query has been addressed.. Can I ask your suggestion for the math I need for this:? The water coming out my steam-condenser is about 150°, my groundwater is about 58°, my 32' long 3/8" copper-inner CFC will drop the wort from boiling to 68° with the tapwater at about 1/3 open, I still have to calculate the actual flow rate in GPM or some such, I know that much, but what would the mathematical formula look like to calculate how long a 3/8" copper coil I'd need to put in the ground to return that hot water at ground temp? I've tried looking it up, but although the concepts are all common and generalized, it gets to complex for my current neurological state to properly comprehend, retain and then apply to this specific application.

 

[Mad Mann]

Since this is a hobby and we love to tinker... I built a closed dual circuit glycol thermal chiller. Attempted to include the rough drawing. I use the PEX tubing portion to bring down the initial boiling temp from ~ 212 to 150 and finish chilling with the homemade AC chiller unit. Year round the temp in the tubing is 65 degrees or lower. The AC unit doubles for temp control on my fermenters. The most expensive part was all the glycol. Might be possible to use water on the buried coil if it is down far enough or it is not susceptible to freezing temps.

 

[Mr. Vern]

@Broken Crow no hijack.. this is the stuff I like to think about and I have the privilege to put this into practice for other processes! The job I have has taught me a lot about heat transfer, gas dynamics, control schemes and has been really fun learning over the past 20 years. Unfortunately I know very little about buried pipe thermodynamics and it appears you do not want to use Rule of Thumb when sizing large systems. For homebrew purposes we may be able to use more generalized data (less than 1 ton).

I come up with roughly 7,020 BTUH to cool a 6.5 gallon boil of 1.060 wort from boiling to 68F. This does NOT include any residual heat left in the kettle once flame or heater is shut off. Judging by my hot kettle I think adding 10% is safe, maybe 15-20% to make 8400 BTUH (Using specific heat correction of 0.9 for wort)

To determine how much copper is needed to remove all of the heat in one pass, so you have ground water temp at the return, I think there are too many variables here to be very accurate (at least for me). The cold side of this equation is your ground properties & geometry, while a 50' coil of copper submerged in 58-68F water will cool a 6.5 gallon batch in roughly 30 minutes, the T.D. will vary widely.

I'm sure there are others around here that can work circles around this. I think you would have to segment the heat exchanger (aka tubing) into multiple sections and calculate those out, dividing more sections for greater accuracy seems tedious and that is unknown territory for me. Below I used 35-65 BTU per square foot and degree F. The range most likely spanning various wall thickness. This heat transfer rate is for hot water to cold water, not agitated.

for 50' of 3/8" copper tube and 68F water temp:
At 212F wort temp you are dumping heat quickly at 24,000 - 41,000 BTUH
At 100F wort temp the heat transfer is down to 5,500 BTUH - 9,000 BTUH

To get to ground water temp I would assume doubling the length will get close... but I would have to really research how to get there. 0 degree T.D. requires a LOT of extra surface area, most designs rely on some T.D. to not have to oversize the heat exchanger so much.

Ill be thinking about this over the weekend!

 

[Broken Crow]

Thank you so much Mr. Vern ! My house was built in 1928 and the basement has a decent sized room as a back extention that was originally the coal-bin. Eventually I'll be turning that into my brew room, but first I need to dig outside down to the footing for some minor seepage. I've been trying to determine if it would be feasible and practical to take a post hole digger to the bottom of the hole, which will reach the 58° level, and drop a few copper coils wound in a similar fasion to the chiller coils for fermenters. (My yard isn't large enough to do a full geothermal coil rig). Looks like you've provided me with enough understandable information and data to start figuring out actual numbers.
Thanks Again!

 

[Ridenour64]

Thank you so much Mr. Vern ! My house was built in 1928 and the basement has a decent sized room as a back extention that was originally the coal-bin. Eventually I'll be turning that into my brew room, but first I need to dig outside down to the footing for some minor seepage. I've been trying to determine if it would be feasible and practical to take a post hole digger to the bottom of the hole, which will reach the 58° level, and drop a few copper coils wound in a similar fasion to the chiller coils for fermenters. (My yard isn't large enough to do a full geothermal coil rig). Looks like you've provided me with enough understandable information and data to start figuring out actual numbers.
Thanks Again!

Did you ever end up burying a coil? I am just now learning about geothermal and I was curious if a 50-100’ could buried several feet in the ground could provide enough cooling power solely for fermentation control. Low 50’s for lagers or higher for ales. Still thinking what this might look like as far as circulating the water (or glycol) into a cooler and then dispersing it from there to the fermenters, or any other possibility.

Obviously couldn’t cold crash to the 30’s but that isn’t important to me.

 

[Broken Crow]

Wow! That was a year and half ago. :0 That's one of my long-term project and unfortunately between money and disability it takes me a very looonnnggg time to do anything. Still thinking through it though, but where my head is at now: I want to try a single experimental coil in the ground just to see what the heat tranfer > soil rate is like.. I know it won't be anywhere near as efficient as the tap-water in my chiller....
Maybe in a few years somebody will find this thread and say; "Hey I did that and it (doesn't) work(s)! For now, I'm still just trying to get my 'accesible' 3V brew rig done.
Thanks for the interest and info though, it's helping me re-educate myself.