If you have no idea what you’re doing when it comes to your HVAC system, then you won’t know what you need when it comes time to pick one out for your home. Whether your home is new or old, it may need a new blower on the system due to its inability to distribute the proper amount of air to where in the home it is needed. If your blower isn’t powerful enough or can’t keep up with the home, you may notice some discomforts.
One of the most common complaints about faulty HVAC systems is that the homeowner is uncomfortable. This is due in part to a lack of airflow throughout the house, delivering only a part of what it’s supposed to. This is what leads a person to start looking for a new blower if that’s the cause of the issue.
It can be difficult to even begin to know where to start, but that’s okay. What you should know is that there are two types of blowers known as the Operating-Point and Operating-Range. The differences are quite obvious once you know how the airflow works. It’s ideal to understand the difference between the two when it comes time to decide which one to choose.
Two Types of Blowers
A very good HVAC system starts with picking a good piece of equipment. The system selected have the capability to push the level of air that the building needs. The blower, along with its abilities, is extremely important to achieving success of a HVAC system, as our ducts sizing is basically based mostly on the features of the blower within the furnace and fan coil unit.
There are 2 general types of blowers that you will see:
- Operating-Range (OR)
- Operating-Point (OP)
The main difference between both becomes clear when thinking about their airflow tables.
The OP blower may decline in airflow as static pressure raises. The OR blower, however, will keep exactly the same (or close to the same) airflow over the variety of static pressure. It achieves this by altering its rotating speed to “match” the resistance it must work against.
The static pressure shouldn’t truly change a lot after any system is installed. (As filtration system get dirty, its static drop will grow. How much increase will change depending upon how much air you’re seeking to undergo the filter. For this reason it’s smart to oversize filters.) So, don’t discover the wrong concept from my statement before, “as static pressure raises.” A part of the HVAC design process requires the choice of the static pressure where the design is based. The idea is we choose the destination point, or “design static,” and after that design the system so that we emerge on target.
Having said that, you’ll observe that there are many static pressure options to choose from if you’re having an OR blower. It’s also essential to learn that an operating-range blower must consume a lot more energy to rotate faster to be able to overcome the extra static pressure. There’s an investment, so to speak, for reaching necessary airflow at a real static pressure.
Flexibility from Blowers
If you use an operating-point (OP) blower, the budget is etched in stone. You’ve a single static pressure alternative, per blower speed setting, that matches one airflow variety. If you overspend your OP static budget, the airflow reduces, alongside efficiency, capacity, and durability. So, the operating-point (OP) blower ASP selection process is influenced by the amount of airflow you should have, together with the blower speed you decide to design with.
Operating-Point Blower Table
This chart displays the blower information for a 1.5-ton fan-coil unit. See that there can be Five different speed controls: 1-5. If our aim was to have 600cfm moving throughout the system, we’d only have two operating-point options. The first option is to get the HVAC blower speed to Med High #4, and design the air duct system to produce a TESP (total external static pressure) of roughly 0.65 IWC. This will allow our blower to transfer the 600 cfm we must (interpolate between 0.60 and 0.70 columns). Another option is to get the blower to the High #5 speed setting, even though setting up a TESP that’s off this chart – probably anywhere in the 1+ range. As the data isn’t listed, this might be a risky option to take. So, we’d be left with a single option. Our accessible static might be 0.65 IWC.
If you use an operating-range (OR) blower, the ASP process is a touch different. You probably get to select it from the number of static pressures on the blower’s airflow data. You’ll note that there’s a restriction to the OR blower’s capability to fight against higher static pressure. Sooner or later, generally around 0.75 IWC (inches of water line), the flow of air will start to disappear, which is often below your preferred airflow.
Manual-D recommends that you simply steer clear of the “top-third” of the blower’s ASP range listed from the manufacturer. My suggestion is to pick the lowest ASP which you are able to do, typically between 0.50-0.75 IWC. Once you lay out the ducts, components, and fittings you are able to adjust your ASP till your FR is inside the acceptable range.
Sometimes, you’ll discover that you might need to use a larger piece of equipment to find a blower that’s sufficiently strong enough to meet your requirements. I often meet this when trying to use small furnaces (40 kbtu) which have large cooling loads (2.5 tons, for example). It’s difficult to get a 40 kbtu furnace that are able to move 1000 cfm at a high static.
Operating-Range Blower Table
This chart demonstrates the blower details for any 120,000 btu furnace. This unit features a variable speed motor that are operating in an operating-range layout. For every single combination of ON/OFF switching shown, the blower will give a different measure of airflow depending on the TESP listed on top of the chart.
When we had a 3-ton air conditioning unit attached with this system, we’d like to deliver about 1200 cfm of air throughout the system. We’d select the ON/ OFF option, with the SW4-3 option shown inside the footnote. This will enable us to offer an airflow amount just shy of 1200 cfm. When selecting the ASP for the Friction Rate calculation, we’d be capable to choose one of the static pressures displayed, if the relevant airflow would fulfill your system’s needs, as the blower will alter its speed so. One thing you should bear in mind is that high static = high energy consume, as the blower is working harder. It can possibly cut the blower’s life-time. My advice is basically begin with 0.50 IWC, altering up as needed till your Friction Rate is inside the ideal range.
Many manufacturers offer a couple of different models for the same capacity (when handling furnaces), which have much stronger HVAC blowers. This gives them to be coupled with larger-sized air conditioning units, which demand larger airflows.