Tag: headmaster

Remote Ice Machines

Why would someone want to take an already complicated machine and make it even more complicated? The answer: human arrogance and engineer’s hubris. (just kidding) Fortunately, thousands of these ice machines have been installed and serviced- let’s take a little overview of a few of the critical differences and things to consider when working on remote ice machines versus self-contained models. We’ll be covering Manitowoc remote series in this article, as other brands usually have very similar setups.

What’s the difference?
Remote Ice Machines are a good option in places where water-cooled ice machines are not a good option due to poor water quality, and self-contained air-cooled machines are neither desirable nor practical- such as restaurant lobbies, kitchens saturated with grease, or in areas where you cannot reject heat without affecting the air conditioning load.

There are several different types of ‘split system’ ice machines. Some have only the condenser coil, condenser fan, and head pressure control valve in the remote unit. Others have the entire traditional condensing unit including the compressor, receiver, and accumulator outside. Higher capacity systems require larger compressors and components which can take up valuable space, which is something many restaurants have a limited amount of.

How do they work?
Almost the same as regular self-contained ice machines. The refrigeration cycle does not change (much) with the addition of a remote condenser or condensing unit. There are, however, some key components added to the system which are not typically present in smaller self-contained ice machines.

Here is a refrigerant piping schematic from a self-contained Manitowoc S-Series Ice machine:

Notice that the refrigeration piping is very similar to a typical refrigeration system, but with the addition of a hot gas bypass line from the compressor discharge line to the evaporator inlet after the TXV. This method is used in the harvest cycle to divert hot gas from the compressor to the evaporator grid to allow the ice to drop. In a remote ice machine, there are several more components.
Some extra components often include:

⦁ Head Pressure Control Valve (Headmaster)
⦁ Accumulator
⦁ Receiver
⦁ Liquid Line Solenoid Valve
⦁ Harvest Pressure Regulating Valve
⦁ Harvest Pressure Regulating Solenoid
Note the differences in the following piping schematic for Manitowoc Remote S-Series machines:

In this diagram, you can see there are some extra considerations to take into account when troubleshooting these remote machines. Since the remote condensing units often are exposed to varying ambient conditions, they must be equipped with a Head Pressure Control Valve (headmaster) to maintain a minimum pressure in the liquid line to the expansion valve (typically 180 psi) in low ambient conditions. The liquid receiver stores “extra” refrigerant to be used by the system in low ambient conditions. If charged correctly, the receiver is designed to maintain sufficient charge in the system to operate down to approximately -20°f ambient. These components are typical in any refrigeration system exposed to wide outdoor ambient temperature swings, but there is a set of parts that are not typically encountered: the Harvest Pressure Regulator and Solenoid.

HPR Valve and Solenoid

During the harvest cycle, the hot gas valve is energized, and discharge gas is piped directly to the evaporator inlet via the hot gas bypass line to assist in harvesting the ice. For this to work, there must be a sufficient amount of heat maintained to be rejected long enough for the ice to drop within the 3-minute harvest cycle. At times, there may not be enough heat to keep the hot gas bypass line warm enough to efficiently harvest the ice in the evaporator, and the high-temperature, high-pressure vapor can begin to condense into a liquid in the evaporator- causing liquid to enter the suction line and the compressor. As we all know, compressors are not fond of trying to compress a liquid; so Manitowoc solved this problem by adding the HPR valve.

During the harvest cycle, the HPR solenoid is energized, allowing vapor from the top of the receiver to meet the HPR valve. The HPR valve is similar to the Headmaster, in that it modulates refrigerant to maintain a minimum pressure. If the suction pressure falls too low during the harvest cycle, we lose the ability to transfer sufficient heat to the evaporator- the HPR keeps the suction pressure high enough through the harvest cycle to maintain the heat required for proper harvest. A simple enough concept, yet often overlooked by many technicians not familiar with remote systems.

Not so different after all

As with any system you are unfamiliar with or don’t have much experience working on, never be afraid to consult tech support or search online for a service manual to read through. Service manuals for all the major ice machine brands can be found online. When it comes to ice machines, knowing the sequence of operations is the key to successfully troubleshooting any make or model. Remote ice machines are not much different from typical refrigeration systems in the way they function. Patience is a must for any technician who has the pleasure of working on ice machines- remember always to be thorough and observant.

— Austin Higgins

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Condenser Flooding / Motormaster Podcast Companion

This article and podcast is courtesy of Jeremy Smith, one of the most knowledgeable and helpful refrigeration techs I know.

It’s my feeling that, no matter how well explained, this topic really requires a treatment that is more in depth and one that can be absorbed slowly with the ability to continually return and re-read certain sections to allow for best understanding of the subject matter.

As discussed in the podcast, as the outdoor temperature drops, the capacity of the condenser increases dramatically causing it to be, essentially, oversized for normal operation.   To counteract that, we use a valve (headmaster) or valves (ORI/ORD) to fill the condenser with liquid to effectively reduce the amount of coil that is actively rejecting heat and condensing refrigerant.   This also maintains a high enough liquid pressure feeding our TEV.   This prevents wild swings in TEV control because it is a pressure operated mechanical device.

First things first, let’s open up Sporlan’s 90-30-1 … seriously go ahead and click it , it will open in another tab so you can go back and forth.

This is a document I reference all the time when dealing with condenser flooding problems.  If you’re tech savvy, save it on your mobile device.  If you’re more of a low-tech guy, listening to a podcast and reading an internet publication on your flip phone or whatever, go ahead and print this out, laminate it and keep it in your clipboard.   Heck, even if you are a high tech guy, sometimes nothing beats a hard copy of this the first few times you work through it.

If ,after the podcast, you haven’t read through this to familiarize yourself with it, take the time to do so.   It seems like a really complicated procedure to work through, and the first few times that you do it on your own, it can be.  With practice, however, you’ll get used to it.

We’ll work through a condenser flooding calculation here in slow time, outlining all the different calculations taken into account.

First lets lay out the basic info we need.  The measurements and counts will vary, of course, depending on the equipment that you have.

If we have an R22 unit, 44 condenser passes ⅜” in diameter each are 38 ¾” long with 42 return bends.   Our evaporator temperature is 20°F, current temp is 35°F and the lowest expected ambient is -20°F.

Now, that seems like a lot of information, but we’ll break it all down.

First, we need to figure the total length of the condenser tubing in feet.   So, we take 44 x 38 ¾ and get 1705” of tubing.   1705 ÷ 12” per foot gives us 142.083 feet of tubing.   Now, that’s just the straight tubing.   We’ve got return bends to account for.

Refer to our Sporlan document.   In TABLE 1, you’ll find an equivalent foot length per return bend.   In the case of a ⅜” return bend, it’s. 2 feet per bend, so 42 x .2 gives us 8.4 feet more.

Add those together for total length of 150.483.  Back to TABLE 1 look in the R22 section under ⅜” tubing and follow the line for -20°F across.   You’ll find a density factor of 0.055.   This number is how many pounds of liquid refrigerant is needed to fill one foot of tubing at that temperature.   So, 150.483 x 0.055.  This gives us 8.28 pounds.  This is the amount required to fill the entire condenser with liquid, but we don’t really need to fill the WHOLE coil….

Back to the document..TABLE 2 this time.

Across the top, find 20° evaporating temp, now follow that down to the -20°F row.   This gives us a percentage.   82%  so, this unit at -20% will have 82% of its condenser filled with liquid.   So let’s take 8.28 x 0.82 to get our flooding charge.

6.78 pounds.

Now, what does this number really mean.   This is the amount of refrigerant we need to add to a system that we’ve JUST cleared the sightglass on when the ambient temperature is 70°F or higher.  If our ambient temperature were 70 degrees or warmer, we could add just that amount past a clear sight glass and walk away, satisfied in knowing that the unit will run properly no matter what the weather throws at it.

Remember, though, that our current ambient is 35°F.   So, now what?

Time to stop.  Get your Sharpie out and WRITE THIS NUMBER DOWN!   Record it on the unit somewhere.  Somewhere easy to see but somewhere that the sun doesn’t degrade the ink over time.   That way, you only have to go through this one time.  If you’re doing a new installation and startup, do the next guy a favor and write both this AND the total system charge down somewhere so that I don’t have to guesstimate the charge when it all leaks out.

Now, let’s go back to TABLE 2 and look at the 35°F row.   We find that at 35°, we need to have 63% flooded.   Well, we’ve got a clear sight glass and it’s 35° ambient so, we’re already 63% flooded.

Since the most we need is 82% flooded, 82%-63% gives 19% so, we take our total, 8.28 x 0.19 to get 1.57 pounds.  At our current conditions, that’s all the flooding charge that we need to add because we’ve already got some flooding going on to have a clear sightglass because we’re under the 70 degree mark and the low ambient controls are in play and doing their job.

Some techs claim that just spraying water on the coil will flood the condenser enough to allow the use of that as a charging technique.    Let’s think about it for a minute.   What variables come into play with a method like that?  Variables that we can’t control…  for starters, what is the wet bulb temperature of the air entering the condenser?  How well is the condenser wetted? With the stakes being what they are, I’m not excited about the prospect of using this because I’m probably going to be the guy who winds up on the roof when it’s -20 and the wind is howling and this unit is low on gas because someone tried to use this method to figure a flooding charge, didn’t get enough gas in the unit and now it’s short.    I’ve still got to my due diligence as a service tech, do a full leak check, not find anything, and walk away wondering if I missed a leak somewhere all because someone else didn’t take a couple minutes to do a little work to do the job properly.  This is a totally preventable service call.

What about TABLE 3, you ask?  Very astute and that tells me that you’re reading ahead. Excellent.  I have never had to use it.

It gives a different flooding percentage for units with an unloader and low ambient controls where they’ll be running in low ambient conditions.  With the unloader, remember that we’re really moving less heat, changing the condenser dynamic and making it even MORE oversized than it would be if there weren’t an unloader, so more refrigerant needs to be added to properly flood the condenser.

— Jeremy Smith

P.S. – You can checkout the Testo 770-3 multimeter we mentioned in the middle by going here

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