A Pumping Primer
The bottom line is that the pump has a substantial effect on system performance; if it’s not working, nothing is going to happen. Of course, sizing, selecting, and installing the pump are all critical aspects if a system is going to work well and keep operating costs to a minimum. But configuring the pump correctly is another factor that can determine whether or not a system operates as planned.
Like designing and installing any hvac system, it’s all in the details. It’s best to do it properly the first time to avoid problems down the line.
The Physical InstallationThe pump installation really is a function of the pump design. For example, base-mounted pumps, by their nature, have to be mounted on a concrete pad somewhere, whereas an inline pump can be mounted in the pipeline itself.
With all pumps, however, there are some generalizations that can be made, according to Roy Ahlgren, director of training and education for Bell & Gossett, Morton Grove, IL:
With base-mounted pumps, one of the biggest problems Ahlgren sees is that they are not properly grouted in place. “By that we mean a non-shrinking cement grout that would bond the pump base to the concrete pad and serve to solidify the whole installation.”
As far as the piping is concerned, it has to be independently supported by proper pipe hangers. In addition, the suction conditions need to be optimal. “The suction piping is often a place where people make mistakes. Single suction pumps very often need a device called a suction diffuser. It’s a device that conditions the flow as it enters the pump impeller. Not all pumps need them, but many end-suction pumps work a lot better and last a lot longer with devices like that.”
On the discharge side of the pump, a service valve and check valve are also necessary, says Ahlgren. That is, unless it’s a very simple system where there’s no possibility of backward flow — then a check valve would not be required. But that’s not the usual case.
Pumping AwayWhen installing a pump, make sure that the pump is oriented correctly within the system. That’s because there is a critical relationship between the pump and the compression tank in a closed loop system. The folks at Bell & Gossett have found that the system operates a great deal better if the pump is pumping away from that connection point where the compression tank connects to the system.
“People still don’t realize that’s the way it’s supposed to be done,” says Ahlgren. “The reason it’s such a subtle point is because with a small pump, you can get away with putting it pretty much anywhere. But when you deal with larger headed pumps, it can make a very crucial difference.”
In addition to pumping away from the connection point, pressures in the system should be kept as high as possible, says Glenn Huse, senior product manager for residential hydronics and engineered specialties, Bell & Gossett. “This provides a lot of benefits, one of which is to help compress the air in the solution and move it back into an area where we can get it out of the process itself.”
One mistake that contractors often make is to inadvertently install pumps in series with one another. This often happens when they try to use primary-secondary pumping techniques and miss some crucial aspect of those techniques. Each pump in a series installation adds its head to the common flow. This is fine if that’s what you’re trying to do. But when engineers are trying to make use of primary-secondary pumping, they may omit that crucial low-pressure drop common pipe, and then they’ll have pumps in series when they didn’t want it.
Reducing Pumping CostsIt seems that no matter which type of hvac system you’re talking about, contractors have a tendency to oversize the equipment. The same is true where pumps are concerned. “An oversized pump is going to possibly create problems in the system in terms of excess velocity and flow noise, and it’s also going to cost a great deal more money to operate over the course of a year,” says Ahlgren.
Besides correctly sizing a pump, another way to save in operating costs may be to use a variable-speed pump. Variable-speed pumps actually change the pump curve, reducing the pump speed at periods of part load, so there’s a reduction in flow. This theoretically results in a substantial decrease in pumping horsepower.
While contractors have usually thought of variable-speed technology for only larger applications, Ahlgren says that the cost of electronics is constantly going down, so he’s seeing the technology applied in smaller and smaller applications. Variable-speed technology is already widely used in radiant systems.
But contractors still shy away from the technology, because many feel it’s too complex. “There’s a lot of benefit that can come from variable-speed pumping. We’re trying to make it simple for an individual to set up, more like plug and play, if you will. Once we get to plug and play on our pumps, you’ll find far more of them utilized,” says Huse.
But whichever pump you choose and however you design and install it, the good part about hydronics in general is that it’s pretty forgiving, notes Ahlgren. “There are a lot of mistakes you can make, and the system will still work at least adequately. The real difference is in making it work at the lowest cost with the least probability of callbacks or trouble. I guess the only advice I would give people is to make sure you keep up to date from a training sense, come to the seminars, read the books, ask questions, and make sure you know what you’re doing.”
Pump Up Your TrainingBell & Gossett has been training people in the hydronics industry since 1954. They believe that the better educated the contractor, the larger the hydronic market will be. To better educate the industry, the company maintains the
Little Red Schoolhouse, a completely equipped learning center in Morton Grove, IL, which has trained more than 45,000 engineers, contractors, and installers in the proper design, installation, and maintenance of hydronic and steam systems.
The company has six different seminars, four of which deal specifically with hydronics and pumping systems. These seminars cover the whole spectrum, from the beginning level to slightly more advanced design, to a very detailed advanced seminar in the design of large chilled water systems.
There are also seminars available specifically targeted for contractors, as well as those who are interested in the operation and maintenance of the systems.
Bell & Gossett also maintains a comprehensive web- site, which includes its very popular “Ask Red” section, in which experts at the company field questions from contractors and others in the industry. Seminar information may also be found on the website at www.bellgossett.com.
Publication date: 10/02/2000