Careful there. Im not too familiar with this process, but atleast in Phase change, you can destroy the cooling system by going too hard on it. You do have to limit the temperature it reaches

Careful there. Im not too familiar with this process, but atleast in Phase change, you can destroy the cooling system by going too hard on it. You do have to limit the temperature it reaches

I know, have a "smart" thermostat to detect any possible issues or stop in temperature change and turn off the cooling.

If the system is capable, it will reach the temperatures you dont want if left to run forever. So any thermostat set to cut out at the correct temperature will really cut it out every so often, and cause the loss Medved described - The output temp will jump up again (and as there are losses in the system going to heat, it can go even above ambient), and second, the cooling process will have to waste again lots of Energy to go all the way again from ambient to the wanted temperature range

So if anything, the smart thermostat must not switch it off, but cycle between high and low power levels or so (when in the low level it cant keep up with the cooling requirement, but does not lose the cold too fast)

Or non smart thermostat along with valves

If the system is capable, it will reach the temperatures you dont want if left to run forever. So any thermostat set to cut out at the correct temperature will really cut it out every so often, and cause the loss Medved described - The output temp will jump up again (and as there are losses in the system going to heat, it can go even above ambient), and second, the cooling process will have to waste again lots of Energy to go all the way again from ambient to the wanted temperature range

So if anything, the smart thermostat must not switch it off, but cycle between high and low power levels or so (when in the low level it cant keep up with the cooling requirement, but does not lose the cold too fast)

Or non smart thermostat along with valves

Inverter drive to the rescue!

Thats the fancy way of doing it, but even simply a motor drive-able at 2 levels is ok

Thats the fancy way of doing it, but even simply a motor drive-able at 2 levels is ok

With a place this fancy, you might as well use the fancy method.

There comes some considerations..

Can you get a pump with such motor ? Not all motors can be speed controlled only through the voltage input. Induction motors for example must be run at low slip conditions to work properly, which means pretty much nearly constant speed, and not that wide range of torques either. Sure if it is not a sealed unit, you can use brushed motors, brushless motors, multiplle motors (such as 2 different induction motors with different speed and power) on a common axis and run one at a time, and so on

If suitable motor setup is not a problem, you might just not need the inverter anyway

There comes some considerations..

Can you get a pump with such motor ? Not all motors can be speed controlled only through the voltage input. Induction motors for example must be run at low slip conditions to work properly, which means pretty much nearly constant speed, and not that wide range of torques either. Sure if it is not a sealed unit, you can use brushed motors, brushless motors, multiplle motors (such as 2 different induction motors with different speed and power) on a common axis and run one at a time, and so on

If suitable motor setup is not a problem, you might just not need the inverter anyway

Then multi stage it is.

Quote from: Medved on July 24, 2016, 04:16:24 PM

The problem of using such concept for general cooling is how to transfer the "cold" from the machinery to the cooled spot efficiently and with the ability to control the temperature (switching it OFF by a thermostat means the machinery will form a heat bridge bringing the heat back into the cooled area, so wasting the energy

Solenoid values breaking the gas path when the pump is off ?

It is one machine, where one part becomes the cold one and the other the warm one. If you take the Stirling example, there are two cylinders with two pistons on one crank shaft, with connecting rods or so. When operated, one of the cylinder gets cold and the second gets "hot". With proper gas this could do easily down to around 100K in a single stage, but once you stop it, there is rather high pressure gas chamber, full of very thermally conductive gas (the consequence of it's ability to work there), so quite good thermal channel leading the heat back. Furthermore the Stirling will attempt to turn into an engine mode, running backwards and by that carry the heat back into the cold chamber even faster.



For the cold room: If the desired experience are heavy frost burns and freezing to death, then maybe. What plays the main role is not that much the absolute temperature, but the difference. So if you start from the Florida's humid 40degC, even the -20degC will be quite huge shock.
And if someone complains it is lame, let him enter with just a T-shirt he is wearing outside...
The regular machinery can make lower as well, but that is really something that requires individual medical supervision, so then we are talking about rather small chambers and not a stadium...

-164 Deg C is the lowest I've seen it's a 128 liters of mind numbing cold, but it would teach the kids not to take my Popsicle with in the first lick, http://www.labfreez.com/laboratory-freezer/ultralow-temp-freezers/MR-DF-ZW-164c-ultra-low-temperature-freezer

you'll need 3 phase power, and it's 3600 watts running and at a guess one compressor maybe two will run 24/7 because this is either a dual or even a triple stage system to get that low so they will use several KW's all day long, and at a guess its about $20 / $30 K plus shipping the 1/4 ton box, but it might be more I know the fisher -86 units are about $15K.. 

What are you thinking about doing that needs to be so cold, If, it's a one off thing have you looked are renting space in a freezer in a lab or just getting a dewar of nitrogen ?

Because generally with most lab stuff you don't need much below -85 and anything cooler just wastes power, but if you need more then -164 C (-263 Deg F)  this freezer offers you will need to move into liquid nitrogen cooling for bulk cooling or move into sterling cryo-coolers (expensive and while they can get crazy cold, like within a few degs of 0 K they can't move a lot of BTU.) or find a  compressor that will use rare refrigerants like  R-704 (Helium ) R-720 (Neon) R-702 (Hydrogen) but every once and while compressors come up in surplus for filing scba tanks that might be able to hit a high enough pressure to play with these refrigerants...   

What are you thinking about doing that needs to be so cold, If, it's a one off thing have you looked are renting space in a freezer in a lab or just getting a dewar of nitrogen ?

It's an idea for an arctic theme park, or maybe have some clever thermostats to make it simulate winter.

An arctic theme park, you better be selling pure moonshine in the park because at those temps nothing else will be liquid..