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#atmospheric pressure

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The amount of pressure you're under depends on where you live. I live in Florida, so I'm very close to sea level. Therefore, the weight of the atmosphere is exerting exactly 14.7 pounds per square inch (PSIA) of pressure on every surface in every direction. There is no such thing as negative pressure—only pressure lower […]

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#atmospheric pressure #hvac #pressure #psi

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Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

In this short podcast from the Bry-X stage of the 7th Annual HVACR Training Symposium, Matthew Taylor from Kalos Services introduces refrigeration pulse valves, which started as a solution for CO2 refrigeration systems and are now common in commercial refrigeration as a whole. He briefly explains how they work and describes their role in the refrigeration systems (and possibly commercial HVAC systems in the future!).

Refrigeration systems have moved away from electronic expansion valves (EEVs), which have been adopted by residential HVAC systems only recently, and have been using pulse valves instead. Pulse valves are also electronic expansion devices with fewer parts than EEVs (which often have stepper motors and complex electronics) and lower failure rates as a result.

Pulse valves have a pressure transducer and a temperature sensor that go on the suction line to calculate the superheat; these report to a controller that takes the data from those parts, calculates the superheat based on the refrigerant and programming, and controls the valve like an EEV. However, there are only two wires, and the controller turns the valve on or off (like a solenoid) instead of sending pulses out. Solenoids just open or close completely, but pulse valves have a port (oversized fixed orifice) through which liquid refrigerant passes; when the load changes, the controller merely sends power to open the valve when the load goes up and stops sending power to close the valve when the load goes down. The valve is open for a certain percentage, and the on/off function is open for that amount of time in a six-second duty cycle (and off for the remaining time); this is pulse-width modulation. They also work well with refrigerants that have glide.

However, pulse valves have some challenges. They may have issues in cases where we have very long evaporators, as there are delays between what happens between the inlet and outlet. Having multiple, shorter evaporators is a common solution to this problem, and these designs are more efficient in general (especially when they can be used with efficient refrigerants that move slowly through the evaporator). Pulse valves also require a computer (though EEV ones are similar), and are less serviceable than other valves; some may require technicians to take the valve apart to take the screen out, which requires replacement O-rings and gaskets. They are also noisy enough for customers to hear them.

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