How to / DIY > Everything else
DIY water chiller - reading suggestions?
BruceM:
This year's fires and record heat have forced my to re-consider adding a water chiller to my in floor heat system for some modest cooling. Since the house is only 1100SF and superinsulated, and based on tests with my neighbor's home using well water, about 12,000 BTU would just do it, and that's within my daytime PV/inverter power of 1500W at 230VAC. I only need to pull out about 4 degrees per day, my hot day heat gain which I normally can overcome with just opening windows at night. But not when smoky or clouds hold in the heat at night.
I've read all about refrigeration systems and understand the principles, but lack hands on experience.
Water chillers are grossly overpriced for their BTUs, using titanium clad heat exchanger assuming corrosive, oxygenated water. My heating system is closed loop, so that's a non-issue and so I'd like to use a tube in a tube or stainless plate type exchanger between refrigerant and the in-floor, recirculated water. This will require new tubing on the low pressure side.
I'd love to find a book or other resource so I can learn how to estimate the amount of refrigerant required after evacuating the assembled system. I would prefer to use a non-inverter mini split outside unit, or modified evaporator window AC unit with 3/8 pipe run of about 6 feet to the plate heat exhanger. Issues I need to learn include when to purge after brazing, how to calculate refrigerant charge and lubricant, how to adjust the evaporator valve for optimal efficiency.
Any suggestions for good texts or websites?
BruceM
I'm looking for the practical experimenter's guide to homebrew refrigeration, I suppose.
mike90045:
way over my head.
But chilling the floor, will the coolness travel up into the house ?
BruceM:
The notion that heat only rises is erroneous. Hold a hot pan just above your hand and feel the heat radiating downward . Transfer is better with lots of convective air flow, but using the floor provides so much area that it's not a problem; there is adequate room air movement to transfer heat from the room air, walls and ceiling to the cooled floor surface.
The use of in floor heat systems for cooling has been well proven. My house is superinsulated and the house temperature is within a few degrees of the tiled, insulated slab floor. In heating season, the floor is never actually warm except near the manifolds. For cooling, you must use water above the dew point, and it will not dehumidify so is appropriate for my high desert climate but not for others. New Mexico state paid for most the early research; they used unglazed night sky cooling panels to help pull heat out of commercial buildings at night. I did experiments with night sky and evaporative cooling a few years ago. I could never quite get water temperatures to the high 50F's, always mid 60's. You need water temperature a bit over near 15F cooler than the desired slab temp to get good transfer.
I'm having trouble finding a 12000-15000 BTU condenser unit drawing under 1500 watts continuous without variable speed inverter drive.
broncodriver99:
Bruce,
I am a Refrigeration/HVAC tech. The trade and technologies within have changed a lot in the last decade. The only book I can recommend is "Modern Refrigeration and Air Conditioning". I am not sure when it was last updated so may be a little thin on some of the inverter technologies but is very good for basic principles. I will say that most Mini Split units will have a proprietary communication protocol between the indoor and outdoor units. They usually require at least a signal from a hall effect sensor on the indoor blower motor to run and will need temp sensor data from the indoor coil as well. You may be able to figure it out having an electronics background but you will need to replicate that signal to get the unit to run. I have had a similar system planned for years but instead of cooling a slab, building an ice bank. I have most of the pieces and parts salvaged from jobs over the years.
I haven't seen a non-inverter mini split in at least 15 years and don't believe they are available unless used so you may have to use a window banger instead. As far as purging practices the best practice is to always be purging especially with the modern refrigerants and oils, they don't like ANY moisture. I use a 2 stage regulator with 2 different low pressure settings to help prevent burning through so much nitrogen. The first is a purge setting which moves a fair amount of nitrogen through the system to displace the air and then switch to a braze setting which flows just enough nitrogen to keep the air out of the system. You want to be bleeding nitrogen the whole time you are brazing and you never want to leave the system open. Always seal it up and add some nitrogen to keep it dry. As far as estimating refrigerant charge that is going to be a big task as there are a lot of variables. The simplest thing to do is install a refrigerant sight glass in the liquid line and charge to a full sight glass with a target of at least a few degrees of sub cooling of the liquid. This is all dependent on the refrigerant you use and operating conditions. The charge is calculable using pipe volumes and density data for the specific refrigerant but in the end you will end up adjusting the charge for proper operation. I would be surprised if the system you are planning is more than 1-2 lbs of refrigerant.
BruceM:
Thanks for the very helpful post, Bronco. I've got "Modern Refrigeration and Air Conditioning", but the 18th edition published in 2004. It is a good one. I'll check for a newer one. Storing surplus summer PV power in an ice bank is a great project that I'd love to read about.
You hit the nail on the head with the inverter type issue for my application. The reverse engineering required is something that I'd rather not do, and the EMI generated by such systems is something I'd like to avoid, despite the lovely soft starting they employ. So it looks like I'm stuck with a window unit.
Does the method of observing the dryer window for refrigerant charge assessment work for R410a? I think most new window AC units are now R410a...but I'm nof sure. If it would work, I'd put in a dryer w/ observation window to make charging easier. I have to research sub cooling and measurement as charge assessment. I recall the term but not how it's done and how to interpret it.
I do remember the important use of nitrogen to avoid oxidization on the tubing interior during brazing/silver soldering. I'll see if I can rent that from my gas/welding supplier.
I also want to thank 32coupe for his PM and speaking with me on the phone about my project. I sure appreciate the technical support!
Bruce
PS- here's an article on in-floor cooling for Mike. https://www.arcticheatpumps.com/radiant-floor-cooling.html
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