Hello everyone, satellite temperature?

[Phase8]

I need a lamens definition for what a satellite temperature is and why it would be needed.
Thank you.

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[jpsmith1cm]

A satellite is an additional portion of the machine that runs at a slightly higher or lower suction pressure.

Typically, the idea is to save energy by only using the capacity that is required to maintain the colder temps or by grouping the higher temperature circuits together and running them at a higher pressure.

[Phase8]

So the freezer in a rack would be a separate circuit from the coolers?

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[jpsmith1cm]

So the freezer in a rack would be a separate circuit from the coolers?

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Actually, the freezers would typically be a different rack.

Think ice cream cases vs frozen food cases.

Ice cream runs a bit colder, but there is typically only a few of them as opposed to frozen.

So, we'd set up a satellite to keep the ice cream at a lower suction temperature.

[Phase8]

So in terms of diagnosis satellite means nothing it technically is its own system?

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[mspanky]

So in terms of diagnosis satellite means nothing it technically is its own system?

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No, a satellite runs it's own suction pressure but shares a common discharge line, condenser, and receiver with other compressors. (rack)

[Joe Harper]

In smaller stores you would have one rack, with low and med tem circuits. The med circuits are controlled by an evap pressure regulator. Could be a sorit, stepper valve, or an ORI.

Since the frame pressure on a 404 low remp rack is around 17-20 psi, you can run a med temp circuit at 60 psi by regulating the applied suction pressure.

[Phase8]

Wow, now I think I can understand it enough to explain it. Thanks everyone.

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[jpsmith1cm]

In smaller stores you would have one rack, with low and med tem circuits. The med circuits are controlled by an evap pressure regulator. Could be a sorit, stepper valve, or an ORI.

Since the frame pressure on a 404 low remp rack is around 17-20 psi, you can run a med temp circuit at 60 psi by regulating the applied suction pressure.

A lot of times, we install a split rack for this application. Loop the liquid line and suction lines and put steppers at the cases.

The little stores LOVE 'em. Save them a ton of money over a dozen singles.

[bunny]

I'm sure you understand compression ratio: The ratio of absolute discharge to absolute suction (with absolute being gauge pressure + 14.7, if at sea level).

The higher the compression ratio, the less efficient the compressor is. This has to do with the amount of piston travel needed to re-expand the vapor that is trapped in the clearance between the top of the piston and the bottom of the valve plate.

So, if you can isolate the system operating at the lowest saturated suction temperature by piping it to its own compressor (the satellite compressor), the remainder of the compressors on the rack can operate at a higher saturated suction temperature, meaning more efficiently. No need to operate the entire rack at -25 SST to satisfy the 24' of ice cream cases. Use a satellite for this, and operate the rest of the rack at whatever the FF cases require...say -15 SST. This translates into less $$ on the power bill at the end of the month.

Here's an example:

A 3D compressor operating at -25 SST and 105 SCT has a capacity of 46,300 Btu. The same compressor operating at a -20 SST and 105 SCT has a condenser 50,500 Btu. That's a 10 increase in capacity, simply by operating at a higher SST.

This is why satellite compressors are employed.

[Jonnyb]

Never see that ? Run a complete low temp rack for medium circuit. For dual temp case ok but not fresh meat.

[Phase8]

Why not fresh meat, why would there be a difference?

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[Jonnyb]

For the post #7
If you have a rack with medium and low temp, you will have to succion group with low temp compressor and medium temp compressor

[jpsmith1cm]

Why not fresh meat, why would there be a difference?

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Because the compressors are burning more energy than is really required.

Smarter to group the circuits by similar suction temperatures and set up the racks that way.

[Joe Harper]

For the post #7
If you have a rack with medium and low temp, you will have to succion group with low temp compressor and medium temp compressor

It all depends on who sets up the rack. You can run all the comps at the same pressure, or run a split suction header, with a common discharge. There are a few different ways to set this up. Running a common suction with regulating valves allows operator to set up defrost cycles to allow low temp cases to pull down after defrost, while med temp cases are going into defrost. The low temp cases can use a majority of the available hp to get back to setpoint.

A good example of what the op was referring to can been seen in Albertsons stores. They have an icecream cake case thathas to be kept at -20f. The low temp rack was di idwd into two main sections. A -12 group (for 0f cases), a -22f group (for -10f cases ex ice cream). The compressors used a split suction header and common liquid feed. Attached to the -22f group was a single compressor that ran the ice cream cake case. The case ran off of the common liquid, but suction was piped directly to the single compressor. Between the cake freezer and -22 suction header was a ori valve. This valve would open when the came creezer came out defrost. It would allow the -22 suction group pull on the case to bring the temp back down, and close off when the load was handled. I think this compressor ran at 10 or 12 psi. On 404a.
This whole system was flawed as the high temp rack powered a subcooler for low temp rack. If the high temp rack went down, so did the low temp. The low temp rack was under powered. Have seen this in 9 different stores. Ice cream is soft beacuse of weak valves on produce rack....

[jpsmith1cm]

This whole system was flawed as the high temp rack powered a subcooler for low temp rack. If the high temp rack went down, so did the low temp. The low temp rack was under powered. Have seen this in 9 different stores. Ice cream is soft beacuse of weak valves on produce rack....

We see this all the time.

Produce high satellite runs the subcooler at about a 37-40 degree evap with a target of 55 degree leaving liquid.

I've got a rack or two that are DEAD without the subcooler and a couple of racks that I'd like to ADD a subcooler to to increase the capacity just a WEE bit.

[Joe Harper]

Ive never understood using the subcooler for capacity. I always thought it should be used for efficiency only..but in not the guy in the choo-choo hat....

[bunny]

It all depends on who sets up the rack. You can run all the comps at the same pressure, or run a split suction header, with a common discharge. There are a few different ways to set this up. Running a common suction with regulating valves allows operator to set up defrost cycles to allow low temp cases to pull down after defrost, while med temp cases are going into defrost. The low temp cases can use a majority of the available hp to get back to setpoint.

A good example of what the op was referring to can been seen in Albertsons stores. They have an icecream cake case thathas to be kept at -20f. The low temp rack was di idwd into two main sections. A -12 group (for 0f cases), a -22f group (for -10f cases ex ice cream). The compressors used a split suction header and common liquid feed. Attached to the -22f group was a single compressor that ran the ice cream cake case. The case ran off of the common liquid, but suction was piped directly to the single compressor. Between the cake freezer and -22 suction header was a ori valve. This valve would open when the came creezer came out defrost. It would allow the -22 suction group pull on the case to bring the temp back down, and close off when the load was handled. I think this compressor ran at 10 or 12 psi. On 404a.
This whole system was flawed as the high temp rack powered a subcooler for low temp rack. If the high temp rack went down, so did the low temp. The low temp rack was under powered. Have seen this in 9 different stores. Ice cream is soft beacuse of weak valves on produce rack....

Not sure what you mean by "this whole system was flawed...."

There is always a "what if" scenario, which can cause an entire rack to go down. What if there's a leak on the LT rack; what if you loose a compressor on the LT rack; what if you loose a condenser fan motor or two in the summer time on the LT rack; etc.

The reason the subcooler is on the MT rack is this: You've got LT compressors operating at between 4-5 HP per ton and MT compressors operating between 2-3 HP per ton. So you use a compressor operating at a much more efficient condition (MT rack) to reduce the mass flow on the LT rack.

You can use a LT compressor to operate the subcooler, but why? You will reduce the mass flow to all of the TEVs on the system, but you're still spending the same amount of horsepower to accomplish it.

And you're right...the subcooler is typically added to increase the efficiency of the system. But on a system that was poorly designed, adding a subcooler (if there's sufficient capacity on the MT rack to add this load) will give the LT rack more capacity. It doesn't make the compressors any more efficient to operate when the system's liquid is subcooled, but it does reduce the mass flow requirement, meaning that less compressor capacity is required.

[jpsmith1cm]

Ive never understood using the subcooler for capacity. I always thought it should be used for efficiency only..but in not the guy in the choo-choo hat....

Fairly inexpensive way to increase capacity.

Couple valves and a HX.