After yet another mishap with my large airbath chamber that was running array of six TEC peltier elements and watercooling loop I've decided to bump up priority on my refrigerator-cooled air chamber box.
In the past life I've built number of phase-change refrigerators for computer CPUs and GPUs to do overclocking, providing cooling down to -30..-40 °C with compact evaporators and heatflux in excess of 300W.
Here task is somewhat similar, but with added twist of precision temperature control need. Also closed-loop refrigerators using phase-changing working medium like freons or other gases are very efficient, far better than TEC elements, so hopefully it will be quieter and more power efficient to operate. After all this concept is how commercial and large industrial temperature chambers are built, with refrigeration units and powerful heaters to maintain precise temperatures. I have Fluke 7015 oil bath designed for resistance metrology applications that using same concept - 500W cooling power refrigerator to precool the 95 litre tank for oil and 1000W of heating elements to provide control and stability. Some photos of my bath are below:
This bath is rather large and heavy, and given the fact that I never had a set of oil resistors remain unused at xDevs labs.
Closed loop airflow to maintain precise control over temperature
Small freon refrigerator in continuous 100%-duty cycle operation to precool the air
Powerful heater with PID controller to increase air temperature to desired setpoint
0.001 °C resolution, hopefully 0.02 °C stability or better
Working temperature range from +10 to +50 °C
Supported heatflux load up to 200-250 W (so we could test power beasts such as Fluke 5720A)
To save some time, I've decided to try repurpose consumer hardware for this project. My buddy Sergiy donated small dehumidifier that is using compact quiet compressor, so we can get ready to use loop out of it.
It was made by Lumisys, model OL12D-D023G and has 115VAC 60 Hz compressor unit, charged with 3.7 oz of R134a refrigerant.
It has bunch of additional hardware like electronics PCBA, some sensors, small -3500 V high voltage supply for ionizing air and relays to switch refrigerator/fan on and off.
I don't need any of that, so after 30 minutes disassembly compressor with all of it's cooling components were extracted out of plastic enclosure.
Now to the business parts. Copper piped radiators are stacked one behind other. White finned is a condenser with dimensions of active area about 180x200x25 mm. Blue finned is evaporator that gets cooled from freon expanding after capillary restriction and has slightly smaller size about 170x170x25 mm. There is just capillary line and copper piping going to both of the elements and it was fairly trivial to bend them and move them in separate spots after all.
After connecting compressor unit directly to my Chroma 61604 AC source output and setting it for 120 VAC 60 Hz, I've got compressor started up right away with inrush power about 1400W quickly dropping to 128-130W within seconds. As system was running temperatures on evaporator quickly dropped to below zero °C and power dropped to about 100 W. I had low speed 120mm computer fan mounted on condenser unit to help with cooling. Evaporator was placed inside of styrofoam box without any airflow fans, just for a test.
After running for 15 minutes system reached terminal condition with evaporator surface temperature recorded at -20.7 °C and power draw from AC source at 97 W. Promising start, and next I'll need to think about enclosure and assembly of this cooling unit, so evaporator could have well insulated space and airflow ducting to accept air intake from the chamber and cool it before entering the heating chamber.
You could 3d print a cowl in two halves snap them over it with a mount for the primary and redundant fans. Hmm. Need an airflow sensor.
Or simply use the insulation board from the local home improvement?
Heat pumps are super efficient. I wish they made the newer multistage heat pumps in these sizes.
If you had both coils in like this: air in --- <> --- air out
Maybe with duct dampers like these: https://www.amazon.com/ZOWZEA…
Doing that you'd be able to leverage the heat pump for both heat and cool and use an electric heater to offset?
After yet another mishap with my large airbath chamber that was running array of six TEC peltier elements and watercooling loop I've decided to bump up priority on my refrigerator-cooled air chamber box.
In the past life I've built number of phase-change refrigerators for computer CPUs and GPUs to do overclocking, providing cooling down to -30..-40 °C with compact evaporators and heatflux in excess of 300W.
Here task is somewhat similar, but with added twist of precision temperature control need. Also closed-loop refrigerators using phase-changing working medium like freons or other gases are very efficient, far better than TEC elements, so hopefully it will be quieter and more power efficient to operate. After all this concept is how commercial and large industrial temperature chambers are built, with refrigeration units and powerful heaters to maintain precise temperatures. I have Fluke 7015 oil bath designed for resistance metrology applications that using same concept - 500W cooling power refrigerator to precool the 95 litre tank for oil and 1000W of heating elements to provide control and stability. Some photos of my bath are below:
This bath is rather large and heavy, and given the fact that I never had a set of oil resistors remain unused at xDevs labs.
Fluke promises stability down to 0.0007 °C for this bath in water which is rather impressive and much better than my airbath would be able to achieve.
Side control and manometer are giveaway sign that this is compressor-based system.
Back to the DIY project now, with desired specs:
To save some time, I've decided to try repurpose consumer hardware for this project. My buddy Sergiy donated small dehumidifier that is using compact quiet compressor, so we can get ready to use loop out of it.
It was made by Lumisys, model OL12D-D023G and has 115VAC 60 Hz compressor unit, charged with 3.7 oz of R134a refrigerant.
It has bunch of additional hardware like electronics PCBA, some sensors, small -3500 V high voltage supply for ionizing air and relays to switch refrigerator/fan on and off.
I don't need any of that, so after 30 minutes disassembly compressor with all of it's cooling components were extracted out of plastic enclosure.
Now to the business parts. Copper piped radiators are stacked one behind other. White finned is a condenser with dimensions of active area about 180x200x25 mm. Blue finned is evaporator that gets cooled from freon expanding after capillary restriction and has slightly smaller size about 170x170x25 mm. There is just capillary line and copper piping going to both of the elements and it was fairly trivial to bend them and move them in separate spots after all.
After connecting compressor unit directly to my Chroma 61604 AC source output and setting it for 120 VAC 60 Hz, I've got compressor started up right away with inrush power about 1400W quickly dropping to 128-130W within seconds. As system was running temperatures on evaporator quickly dropped to below zero °C and power dropped to about 100 W. I had low speed 120mm computer fan mounted on condenser unit to help with cooling. Evaporator was placed inside of styrofoam box without any airflow fans, just for a test.
After running for 15 minutes system reached terminal condition with evaporator surface temperature recorded at -20.7 °C and power draw from AC source at 97 W. Promising start, and next I'll need to think about enclosure and assembly of this cooling unit, so evaporator could have well insulated space and airflow ducting to accept air intake from the chamber and cool it before entering the heating chamber.
You could 3d print a cowl in two halves snap them over it with a mount for the primary and redundant fans. Hmm. Need an airflow sensor.
Or simply use the insulation board from the local home improvement?
Heat pumps are super efficient. I wish they made the newer multistage heat pumps in these sizes.
If you had both coils in like this: air in --- <> --- air out
Maybe with duct dampers like these: https://www.amazon.com/ZOWZEA…
Doing that you'd be able to leverage the heat pump for both heat and cool and use an electric heater to offset?
Just random ideas.