High duct-static pressure creates problems during a building fire when fire dampers close. Closed fire dampers cause downstream duct sensors to detect a drop in pressure. The duct pressure sensors in turn send signals to crank the air handler even faster to get back up to normal operation. Because the fire dampers are closed, when the air handler ramps up, the duct pressure upstream of the fire dampers will increase to a point where a high static pressure switch will cut power to the VFD (variable frequency drive) and send a signal to the DDC (direct digital control). Switches in this application — by specification — are all manual reset and require two outputs: one for cutting power to the VFD and one for sending the signal to the DDC.
Traditionally, there have been three tactics to address this issue, each with its own problems. Continue reading “Solve High Duct-Static Cutout Problems with the Series 1831”
Stability is defined as a change (or lack of change) in accuracy over a period of time.
Drift is commonly used as a specification to illustrate the stability, or change in accuracy over a period of time, commonly shown as X%/year where X = a number; i.e. 0.25%/year. In this scenario, a device with a ±1% accuracy, would be expected to have an accuracy of ±1.25% (1%+0.25%) after a period of one year. Depending on the design, brand, and range of the sensing instrument, the stability can vary widely. Continue reading “What is Stability and Why is it Important?”
Are you having problems with your current lift station level controls? Dwyer Instruments may just have the cost effective solution you need. In this article we will review several level sensing strategies, the advantages and disadvantages of each, as well as an option you may want to consider for your next project.
Lift Station Basics
In an ideal gravity fed wastewater collection system, sewage would flow downhill from its point of origin in residential or commercial areas to its final treatment plant destination. Due to a number of factors including total distance, topography, geology, economics, etc., the ideal piping design is not always feasible. Therefore, in most cases, sewage flows downhill to a lift station where it collects and then is pumped to a higher elevation in order to begin its downhill journey again. Continue reading “Lift Station Level Sensing”
There are several reasons why a 38R is a great choice in your heating or cooling applications, with the most obvious being that there is no power required. The 38R temperature regulator is a fully self-contained unit, requiring no external power source. This could mean substantial savings over the operation of other types of valves.
Regulation takes place when the sensing bulb is exposed to changes in temperature. The thermal system is charged with a predetermined amount of vapor fill, which, when heated, will cause a bellows within the unit’s actuator housing to expand. As the bellows expands, it compresses a return spring while simultaneously moving the valve stem downward to stroke the valve.
When the process temperature decreases or in the event of thermal system failure, the return spring will move the valve stem upward to the “out” position. Continue reading “Why Choose a 38R Self-Acting Control Valve?”
Most local regulations for indoor air quality are designed around ASHRAE Standard 62. This standard specifies the minimum amount of outdoor air flow into an occupied space to be between 15 to 60 CFM per person, but more commonly building regulations require 15 to 20 CFM per person. Besides actually measuring the air flow, ASHRAE also defines indoor air quality using the concentration of carbon dioxide gas in the air. Carbon dioxide is recommended to be less than 1000 PPM. When sizing the air handling unit for a building, engineers will make the design exceed the maximum occupancy in the building or space to ensure that they will always be able to meet the minimum air requirements. In most cases, buildings or mix used spaces rarely are occupied at these maximum levels, thus the amount of conditioned air supplied is usually much greater than what is required. As building owners aim to reduce energy costs and operate buildings more efficiently, wasted energy of conditioning unneeded outside air has been a good place to start. Continue reading “Energy Savings from On-Demand Ventilation”