If you're looking for a single 'best' Bitzer compressor for your ammonia refrigeration system, I'll save you some time: there isn't one. Not really. I learned this the hard way a few years back, and it cost us about a week of downtime and a fair bit of embarrassment.
Honestly, the question 'which Bitzer compressor should I buy?' is kind of like asking 'which vehicle is best?' You wouldn't put a Formula 1 engine in a delivery truck, right? Same logic applies here. The 'best' compressor depends entirely on what you're trying to do. Let's break this down into the three most common scenarios I've run into.
Scenario 1: The 'Set It and Forget It' Refrigeration Plant
This is your typical cold storage warehouse or food processing facility. The load is relatively stable, the system runs continuously, and everyone's main concern is reliability and total cost of ownership over a 10+ year lifespan.
What You Usually Think You Want
The biggest screw compressor you can afford. Bigger means more capacity, right? That's what we thought. We spec'd a massive twin-screw unit for a new cold store back in 2020. It was a monster.
What You Actually Need
For a stable, continuous load in ammonia, the real enemy isn't capacity—it's part-load efficiency. Your system will rarely run at 100% capacity. Most of the time, it's humming along at 60-80%. A giant screw compressor running at part load is just an expensive way to waste energy and wear out your slide valves. (I still have the energy bills from that Q3 to prove it.)
What I'd recommend now, after that expensive lesson: start with a high-efficiency reciprocating compressor from Bitzer for the base load. Something like a V-type reciprocating compressor is often a better fit. Then, pair it with a smaller screw compressor for peak loads. The recip handles the humdrum, steady-state work with better efficiency at lower loads, and the screw kicks in when the doors open and the forklifts start driving in warm product. It's a 'horses for courses' approach. You get the reliability of the recip and the peak capacity of the screw, without the part-load penalty.
Side note: People assume screw compressors are always more efficient. The reality is they are more efficient at full load. At 60% load, a modern recip can easily beat a screw on energy consumption, especially in ammonia applications where discharge temperatures are not a concern.
— From a comparison of our Q1 and Q2 2023 performance data, using the exact same plant load profile.
Scenario 2: The 'Stop-Start' Processing Line
This is common in the food & beverage industry with batch processes. Ice cream hardening tunnels, cheese vats, brewery chilling. The load is high, then it's zero. The compressor starts, stops, starts, stops.
What You Usually Think You Want
Another big screw compressor, probably with a Variable Frequency Drive (VFD) to handle the load changes smoothly.
What You Actually Need
A VFD on a screw compressor for a stop-start application is like buying a sports car to drive in city traffic. You're paying a premium for a feature you'll rarely use effectively. Starting a screw compressor, even with a VFD, is a big electrical event. It takes time to ramp up. And the frequent starts can be rough on the slide valves and oil management system.
The better solution for this scenario, which I wish I'd known earlier, is a multi-unit setup with a group controller. Instead of one big VFD screw, use two or three smaller Bitzer reciprocating or scroll compressors. They can start and stop quickly, individually, to match the load. For example, on a brewery's chilling system I helped fix last year, they replaced a 150kW VFD screw with three 50kW recips. The system capacity is the same, but the response time dropped from minutes to seconds, and the energy bill fell by about 18% (my rough calculation based on their 'before' and 'after' meter readings).
The control logic is basically: 'First one starts, if load increases, second starts, if load drops, first stops, second keeps running.' (note to self: I still think we should have added a fourth unit for redundancy, but that's a different story). The key here is capacity matching through unit sequencing, not through compressor modulation.
Scenario 3: The OEM Machine Builder
You're building a chiller, a condensing unit, or a process cooler. Your customer has the final application. You're specifying the compressor that will be the heart of your machine.
What You Usually Think You Want
The smallest, lightest compressor that hits the spec. Because you're selling on machine footprint and price.
What You Actually Need
You need a compressor that's easy to integrate, has good parts availability, and is reliable in a variety of unknown conditions. From a field service perspective (having had to unf*** a few OEM installations), the biggest problem is when an OEM picks a unique, unusual compressor model just to save a tiny bit of space or cost. Then when it fails, finding a spare part is a nightmare.
My advice to OEMs is actually pretty simple: pick a compressor platform from Bitzer that has a proven track record in your specific application. Don't reinvent the wheel. For a condensing unit for a supermarket freezer, a semi-hermetic reciprocating compressor is a workhorse. Easy to service, parts are everywhere. For a larger process chiller, a screw compressor package from an OEM like Carrier or Johnson Controls might be your best bet, but on the compressor side, a Bitzer screw with an Oil Management System from a supplier like any reliable aftermarket supplier is a safe bet. Don't try to be a hero. use a model that has a shared parts platform with other common Bitzer compressors. (Note to self: I really should create a database of 'compatible spare parts' for the models we see most often.)
So, How Do You Figure Out Which 'Scenario' You're In?
It's not as hard as it sounds. Ask yourself one question: What does my load profile look like over a typical 24-hour period?
- Flat and stable? You're Scenario 1. Look for a high-reliability recip with a small screw for peak shaving.
- Spiky and unpredictable? You're Scenario 2. Look at a multi-unit arrangement with fast-starting recips or scrolls.
- You're building something to sell? You're Scenario 3. Pick a common, service-friendly workhorse.
The bad advice is to call up a salesperson and say 'I need a compressor for a cold storage.' The good advice is to have your load data ready. If you don't have it, that's the first problem to solve, not the compressor selection. Trust me on this one—I learned it the expensive way.
