Fogco has been designing innovative products for the outdoor cooling and humidification markets for over two decades. Sometimes it involves a completely novel idea; other times it is simply an improvement to what already exists. Either way, it is a commitment to excellence that has resulted in Fogco being a perennial leader in the misting industry.
Over the last couple of years, Fogco has been focused on humidification applications for many different industries. These industries include textiles, paper processing, woodworking, wine storage, and greenhouse humidity control. In all of these applications, increased humidification is required for maximum results from the product and/or the equipment that is used.
The Challenges of Multi-Zone Misting
In many cases, to effectively control the humidity system, multiple zones are required. This allows for a “staging” of the mist system so that just the right amount of increased humidity can be introduced into the air at the precise time and in the proper area needed. This multi-zone mist system design does provide for improved performance but it also presents a few challenges.
When a high pressure pump is built for a specific flow, it must create that flow when it is operating. If the mist system has multiple zones and only one of the particular zones is required at a given time, the standard misting pump will still create its rated flow but it must internally bypass all the unused water. This process creates heat within the misting pump and can cause premature failure of the pump seals or other critical components. In addition, the large pump is using electricity that would otherwise be unnecessary and this is seen as a waste of company resources.
One solution is to provide multiple pumps for a system that requires multiple zones. Although this solution does allow for a series of pumps to pressurize the exact amount of moisture that may be needed at any given time and it does ensure that only the amount of electricity that is needed is actually consumed, it is costly and cumbersome and dramatically increases the amount of maintenance time required for a system.
The preferred option is to design the mist system to include a variable frequency drive (VFD), also known as an inverter drive pump. These unique controllers have the ability to change the operating speed of a motor so that one properly sized and designed pump can be used to operate a multi-zone system with flows that vary from 5% to 100% of the pumps total designed flow rate.
The Advantages of a VFD Pump for Your Misting System
The advantages of these VFD designed systems are significant. In addition to the elimination of the need for multiple pumps, the VFD has many different built in capabilities that can be used to enhance the operation and performance of the misting system. Once of the most significant advantage, however, is the cost savings that the VFD provides. Because of the way that the VFD operates (it essentially synthesizes the required alternating current by using a direct current), it can deliver the required power to the motor much more efficiently using as little as 10% of the required wattage when compared to a system that incorporates a 1-pump option.
Obviously, the initial cost of a VFD system is higher than a comparable single pump option, but over time the cost savings can be significant and usually pay for themselves within a year. If your system requires multiple zones and you think it might be worth considering a VFD design, talk to our Customer Service Department and let us help you determine if it is right for you. It may be much less expensive over time than you expected.
How Do VFD Pumps Compare to Other Pump Types?
There are two other basic design options when it comes to misting pumps: direct drive pumps and pulley drive pumps. A direct drive misting pump will usually be the least expensive (except in some cases with sizes above 3gpm), but will also be the loudest because the motor and pump will both be spinning at full rpm (1750 for standard 60 Hz 4 pole motors and 1450 for standard 50Hz 4 pole motors).
A pulley drive is typically more expensive than a direct drive because it includes two pulleys and a belt, and requires either an enclosure or a belt guard. A pulley drive misting pump will also include an oversized bare pump (the standard 1 gpm pump utilizes a 3.8 gpm bare pump) to slow down the rpm of the pump and still achieve the necessary flow.
Most pulley drive misting pumps include additional components compared to direct drive units, which contributes to its higher cost basis. These components add function and feature to the pulley drive pump design. We use a full enclosure (except in tabletop designs, which already include a separate control box) because it provides a place for us to include various custom electrical components without having to provide a separate control box, and eliminates the need for the belt guard.
Even though the motor in a pulley drive unit will turn at full rpm, it will always be quieter than a comparably sized direct drive pump, as the pump is turning at a slower rpm than the motor and creates less vibration and less mechanical noise. The pulley drive misting pump also produces less noise because it is typically fully enclosed where the direct drive pump typically is not.
More Reasons to Choose a VFD Pump
A variable frequency drive mist pump is the most expensive option, but it does have some unique and valuable characteristics. First, it consumes between 20% and 25% less electricity to operate a VFD system than a non-VFD system, due to the inclusion of the VFD inverter and the way it utilizes electricity. This is only the first of three electricity-related efficiencies associated with a VFD mist pump, but it is the primary reason VFD units are desired for many commercial and industrial applications.
Because of the pressure transducers in VFD misting pumps, the system has the unique capability of only turning the motor at the required hertz based on the flow demand at any given time. This unique feature provides a variable operating speed for the motor. In most cases, the motor and the pump are both spinning at an rpm level that is less (usually much less) than a standard direct drive or pulley drive unit. The result is not only a substantially quieter operating mist pump, but a mist pump that requires less electricity to operate. This is the second of three electricity-related efficiencies associated with a VFD misting pump.
As an example, if a 2-gpm system used a direct drive pump, both the pump and motor would turn at 1750 rpm. A pulley drive unit would require the motor to turn at 1750 rpm, but the pump would only turn at about 920 rpm (using a bare pump that provides 3.8 gpm at 1750 rpm). A VFD unit would allow the motor AND the pump to both turn at 920 rpm (using a bare pump rated at 3.8 gpm at 1750 rpm).
The result is that the direct drive would be the loudest; the pulley drive would be quieter than the direct drive; the VFD would be significantly quieter than the pulley drive. This scenario and explanation do not take into consideration other on-site conditions that may affect the noise levels, but it is a good standard to measure when considering the noise levels associated with a direct drive, pulley drive, or VFD mist pump system.
As system flow requirements increase, the VFD will progressively increase the speed of the motor until the pump is providing the required flow to achieve the required 1000 psi pressure. As this motor speed increases, so does the noise level. If the motor and pump spin at full hertz and rpm (60 and 1750 respectively) due to the maximum flow requirement, the noise level could be equal to that of a direct drive or pulley drive unit. However, because the VFD unit affects the speed of the motor, it is always possible to resize the VFD unit to never spin above a desired rpm.
Other than the power consumption savings on commercial or industrial systems — and not accounting for any noise level considerations — a VFD is typically used for multiple zones with less than 50% (and as low as 5%) flow capacity. In these cases, the VFD can manipulate the power supply to the motor, thereby affecting the motor rpm and resulting in a flow output that exactly matches system requirements.
That means there is no bypass in the system. Since there is no excess water being pressurized and bypassed, there is no heat buildup in the pump’s water supply, so damage is eliminated. This allows the system to operate more efficiently because the pump is not overworking itself by producing excess pressurized water. This is the third of three electricity-related efficiencies associated with a VFD mist pump.
Now that you know the three options available for mist pump design, remember that each has its own characteristics that make it appropriate for a given project. The most appropriate option should be determined based on the needs and desires of the end user. To learn more, or to get started with your own misting system, contact Fogco today.
The vfd system includes a DC power supply. This power supply provides power to the pressure transducer which in turn sends a 4-20ma signal back to the vfd to indicate the existing pressure in the system. If the pressure decreases in the system below the programmed set point (1000 psi in most cases), it indicates an increase in flow in the system and the vfd detects this and increases the hertz output to the motor causing it to speed up. As the motor speeds up, the flow output fromt he pump increases. Once the flow equals the demand, the pressure will increase. Once the transducer signal indicates to the vfd that 1000psi has been achieved, the vfd stabilizes the hertz output to the motor to maintain the pressure output. The reverse happens when the flow demand is decreased (as when a zone is closed).
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The pressure transducer is powered by DC power. It sends a 0-10VDC or 4-20 mA signal back to the vfd depending on the pressure it is sensing. This sliding scale of return signal to the vfd is then interpreted by the vfd as a given psi and the vfd reacts by increasing or decreasing the hertz output to the motor accordingly.