Pressure Boosting Systems are essential for delivering water to high-rise buildings; however, the method for sizing these systems has not changed significantly in over 50 years! Cougar USA’s High-Performance Design approach combines our extensive knowledge & experience with the best products on the market to deliver systems that provide constant water pressure with little to no downtime and the lowest Life Cycle Cost. Check out this three-part Tech Talk series on Booster System Design to see how we do it. We will cover the flow and pressure requirements of a building and pump & system selections to meet them.
Pressure Boosting Systems Design Part 1 Tech Talk Transcript:
Hi, I’m Tim Zacharias with Cougar USA on this Tech talk, this will be the first of a three-part series for sizing and selecting pressure boosting systems. On this one, we are going to be looking at the flow rate for a commercial building.
Now, a couple of different things that we need to take into account when we are looking at flow. The first place that we can start is Hunter’s curve in the fixture unit counts. This is a method that goes back to the 1960s. Basically, we can count up our fixture units in the building, look at the chart for what that says the equivalent flow rates are, and what that is going to give us is our worst-case flow rate for that building.
So if every fixture were to turn on and we needed that flow rate, what does that give us in terms of flow?
Now, the floor in Hunters curve is that it doesn’t take into account the diversity of usage and we’ve done flow audits on commercial office buildings, with and without cooling towers, we’ve done hotels, we’ve done hospitals, other types of buildings. And consistently we found that most of the time the usage is about 15% of what our worst-case scenario is for that building, meaning, 75% – 80% of the time we’re running at a partial load condition that is about 15% of what curve is predicting. Now, what that looks like on a pump curve, if we have our flow and head of our pump curve, is that if we were designing to this duty point here, that if that is our duty point, our design, you know, based on Hunter’s curve, really what we are going to see is an operation back here most of the time. This is where our partial load is going to be. So we really want to focus on the partial load condition when we’re selecting our pumps because that’s what they’re going to operate the most, that’s what we wanted to be most efficient because the pump that we select for this duty point is not going to be efficient or operate well at this point.
The other thingS that we have to take into consideration are any sort of special applications. Now, the number one in a commercial building is going to be make up to the cooling tower. Cooling tower, especially a commercial office building, even potentially in a hotel or other type buildings make up to the cooling tower is going to be the number one consumer of water, maybe anywhere from 20 to 80 or 100 gallons a minute, depending on the size of the cooling tower, the makeup line, the type of fill valve that’s used to make it up, but we need to take that into account when we are looking at our worst-case scenario in terms of consumption. So definitely want to make sure if we’re making up to the cooling tower that we have that covered.
Other things that could have large instantaneous demands, kitchens, dishwashers, you know, you could have sterilizers in the hospital, you could have a big sudden demand of all of these things if you have any sort of specialty processes in the building, you want to account for those and plug those into your worst-case scenario.
But if we’re talking, you know, very simple building, just has cooling tower, you know, men’s and women’s restrooms and a little kitchen on each floor, this 15% of our worst-case scenario is going to be a pretty accurate way to go when you’re determining your flow rates.
So, again, if we were to say that Hunter’s curve said that we needed, let’s just say it’s a simple building here, one hundred gallons per minute. You know what we’re really going to be wanting to design to is back in this 15 to 20 GPM range here.
All right. So we’re going to have two other videos as part of this to cover the pressure selection and then ultimately the pumping system selection for pressure boosting applications. So please check out those videos or reach out if you have any other questions.