Hot Water for Dairy Farms
The milking process is a lot more complicated than you would think.
Doing business here in the rural areas of South Central Pennsylvania, we find ourselves surrounded by agricultural operations. As you drive through the gently rolling country side, bordered by the Appalachian mountain range, you will see greenhouses, acres of produce fields, and every time you turn the corner, another dairy farm. There are only about 50,000 dairy operations left in the continental U.S., and it feels like they are all here in my backyard. Most of them are smaller family operations, but more and more of them are becoming commercialized and milk hundreds of cows, three times a day.
The one facility that I visit frequently for boiler maintenance, milks cows 24 hours a day, 7 days a week. The milking is all done via robots. Each cow has a computer chip attached to its ear. As they come through the milking station, the computer reads the chip and knows the cow by name. It then feeds that cow according to its predetermined, personalized diet. As it is being milked, the computer monitors the amount of milk and also if there is any mastitis present in the milk. If anything is off about the cow's milk production, the computer will automatically switch gates and redirect that cow into a sick pen, where it will be cared for by the farmer.
All that is pretty cool.
It amazes me how technologically-advanced the dairy industry is, considering the limited market of 50,000 customers.
There is one truth in all this though, the more technology a system has, the more things there are to go wrong. This is true almost anywhere. There are many things that can bring a dairy to a grinding halt very quickly and cost the farmer big bucks if not remedied right away. One of these is hot water for washing and sanitizing the milking equipment. Having a robust hot water production system is essential for these operations. Its primary purpose is to clean and sanitize the milking equipment and pipelines. Its secondary purpose is to provide heat for the concrete slabs and prevent manure slop from freezing to the surfaces during the winter. The third function is to provide heat for the mechanical rooms, offices and milking parlors.
The wash cycle for milking equipment is an interesting and complicated process. It consists of three cycles. The first cycle begins immediately after the milking is completed, before the pipelines have a chance to dry. It is a rinse cycle, with the typical water temperature around 100 F to 110 F. If the water is too hot during this cycle, it will cause denaturation of proteins in the milk residue, and result in a protein film on the surfaces of the piping. Water that is to cold will cause the fats in the milk to crystallize and leave behind a greasy, hard-to-wash surface on the pipe walls. The second cycle follows right on the heels of the first rinse, and uses the lion’s share of the hot water needed for all three cycles. This cycle needs 170 F water to start, and is not allowed to drop below 120 F by the end of the cycle. The hot water will typically be mixed with some alkaline cleaners. This cycle is considered the wash cycle and lasts about 6 to 10 minutes. The third is the sanitation cycle. It is a cool, acidified water rinse. The water will typically have a pH of 3 to 4 and is meant to remove all traces of the cleaners used in the second cycle.
The whole process will typically take less than an hour, and it uses quite a large amount of hot water in short order. Different setups have different requirements, but some of the larger ones I work on, have a 1-inch pipe from the water heater directly to a large stainless tank where the cleaning chemicals are mixed. The pipe opens and closes via a solenoid valve to fill the mixing tank with hot water. It is nothing to see a 100-gallon water heater depleted in minutes. The water solution from the mixing tank is then pulled through the milking system via a rotary vane vacuum pump. There is an air injector in the pipe just upstream from the mixing tank. The air injector opens and closes while the water is being pulled through, causing water surges through the pipeline and promoting better cleaning. The water needs to move through the pipelines with a minimum velocity of 5 feet/second, to get the proper turbulence and scrubbing action on the sidewalls of the piping.
This cleaning process is incredibly important to a dairy operation. If anything is wrong with the process, bacteria will start growing almost immediately. This can cost the farmer a lot of money. If the bacteria counts get to high, the milk company will fine the farmer for a portion of the payment they would otherwise have received for their milk. If the count is very high, but they catch it in time, they may have to dump their entire bulk tank of milk. Worse case scenario is that it doesn’t get caught in time, and the farmer has to pay for the entire tractor trailer load of milk. That’s a lot of money!
Most of the hot water generation setups I have been seeing lately on dairy farms are an incorrect application of modern technology, and the farmers are suffering because of it. A setup will normally consist of a preheat tank followed by an indirect water heater that is coupled to a ModCon boiler. The preheat tank is first in line and collects waste heat off the refrigeration system that cools the milk in the bulk tank. The water then goes into the indirect heater and is heated to 170 F.
The indirect tank poses the problem, due to the high water temperature requirement. The boiler has to be run at 190 F to get any kind of heat transfer to the water heater. This only gives you a 20-degree TD between the boiler water and the tank set point. This makes the recovery time very slow. With that being the case, the water heater has to be sized to hold the capacity, equal to the gallons of water used in the milking equipment’s wash cycle. It’s not a very efficient way to do things. It requires a tremendous amount of storage, and the boilers do not do well running at those temperatures continuously. The setups I keep seeing, typically will have an undersized boiler for the DHW load, and are grossly oversized for the connected space heating and slab warming loads.
A much better way to do it is to install direct-fired water heaters with large burners. This allows much faster recovery after a tank draw down. In a boiler/indirect setup, you are limited in production due to the heat transfer process. The heat from the flame transfers to the boiler water, which is then transferred to the DHW in the indirect. Each step of heat transfer requires a temperature differential for the process to o ccur. The greater the temperature differential, the faster the transfer will occur. With the DHW setting at 170 F, this doesn’t give enough of a temperature differential to transfer heat at the speed required to meet the demands, in most cases. With a direct fired water heater, the heat from the flame is transferred directly into the 170 degree DHW, and the transfer can occur much faster, allowing the burner to run at max capacity and greater efficiency. This will greatly increase the “first hour rating” of the water heater over the capability of an indirect water heater. That allows for smaller storage requirements, saving space and money. The space heating and slab warming zones can then be satisfied via a flat-plate heat exchanger tied to the water heaters. That prevents short cycling of the burners when there is only a demand for space heating.
So if you get hired to install a hot water production and space heating system for a dairy farm, these are all things that need to be considered before selecting your equipment. They will not be your customer for long if you can’t give them a reliable source of hot water.
I recently got called out to a dairy farm that was experiencing an elevated bacteria count in their milk. The milk inspector had already diagnosed the problem as insufficient hot water during the wash cycle. The company that maintains the milking equipment had already been on seen and determined that it wasn’t caused by any of their equipment. When I arrived, I was met with the setup as seen in Pic A. The water heater is a 95-gallon Phase III Triangle Tube indirect. The boiler is an HTP MC 120. The boiler is incredibly undersized for the indirect heater.
So the troubleshooting begins. As always, it begins with verifying the customer’s complaint. The farmer was able to do a wash cycle for me, and I measured water temperatures from the heater’s output. The water started at 165 F but very quickly dropped to 140 F, even before the second cycle began. Definitely not the way it should be even with the mismatched equipment. I was also monitoring the boiler while we were doing this. The boiler was modulating at about 25 percent, and the delta-T between the boiler supply and return pipe on the Phase III was only about 10 degrees.
My next discovery was that the boiler supply going to the Phase III was actually at a lower temperature than the boiler loop. It didn’t take long to figure out why; there was a Taco 007 being used as the boiler pump. “007s seem to be the universal pump that are just right for every application”(sarcasm). The 007 was not moving as much water through the boiler as was moving through the secondary loop. This caused the secondary loop to run at a lower temperature and the boiler to not be able to run at full output.
I also found the temperature control knob on the water heater turned up to the max. Typical. Just like homeowners turning the thermostats higher in a vain attempt to make the house heat faster, people will turn a water heater to the max in an attempt to get more hot water. Problem is, the max setting on the water heater is high enough that it generates a constant call to the boiler, which was set at 180 F. Which brings me to the boiler control; it was still operating on the factory settings. 180 F set point with a 30-degree differential. That differential allows the boiler to drop to 150 F, 20 degrees below the required temp for DHW, before restarting the burner.
So after correcting all the settings and installing the proper-sized boiler pump, I decided to clean the DHW side of the Phase III. I wanted to clean off any scale deposits from the inside of the heater. I cut open the supply and return pipes and installed purge valves. I am of the opinion that every device that generates high temperature DHW needs to have purge valves installed for cleaning. You will need them sooner or later. As I was installing the valves, I noticed some mineral deposits on the one copper joint coming out of the water heater supply. I thought “uhh-oh,” but not having the correct fittings on the truck to make the repair, I decided to proceed with the cleaning and run to the supply house while the heater was being descaled. Efficient use of time, right? But unfortunately, that wasn’t to be. I wasn’t running the descaler through the heater for more than two minutes before that fitting began squirting out water like geyser.
I told myself I did the right thing; my plan could have worked.
So now I have to replace the supply pipe on the heater, and I only have a little bit of time to get it done before the next milking. I removed the offending section of pipe from the heater supply and found this!
The dip tube for the heater was stuck up in the supply pipe. While all the rest of the issues contributed, this was the main perpetrator to the lack of hot water.
After a quick trip to the supply house, I had what I needed to put everything back together and clean the heater. As I worked, I reflected on my earlier failed plan due to the leaking fitting. My disappointment had turned into what I considered a win. Funny how things work in our favor sometimes.
After the dust settled, I checked in with the farmer. His bacteria counts have dropped to a lower level than they have ever been before. That’s good for everyone.
Harvey Ramer is the owner of Ramer Mechanical (RM) LLC. RM specializes in radiant heating and hydronic heating systems. The company also provides other mechanical services to the residential and light commercial market. Ramer also provides heating system design services and consultation across the country.