Recent content by MNMaint

I was hoping to get some insight on why face velocity was an issuein a refrigernat coil to learn something. I , personally, like to know the science behind what's happening that affects equipment I'd be responsible for. Anyone else out there have something constuctive or educational to add?

In future applications, I'd suggest considering one AHU with two or more direct drive fans in parallel with dedicated VFDs for each fan motor. Direct drive = no belts to maintain or break. The fans do not have to be sized for 100% airflow each at 60Hz either. As long as the drives are allowed...

I've got a dual compressor, dual circuit DX rooftop unit with equally sized compressors. Its currently a constant volume unit but I would like to convert it to a VAV unit. The manufacturer says that because the two refrigerant coils are intertwined, they each have the full face area of the two...

Thank you. Very good start. The set point lock outs should be adjustable, though. In particular, where the elderly are involved the 72 deg F limit for heating imposed by these thermostats simply won't suffice.

Hello, I'm looking for any reccomendations for residential thermostats that are non-programmable and allow for limits to be set on the set points. This is for a rental apartment building where the tenants do not pay for heat. The thermostats would control a zone valve. I've trolled the web...

Hello, I have an installation where shielded 18/2 cable was used to deliver 24V power to a control actuator. The installer used the shield as the ground. Is this code compliant? If so, is it otherwise acceptable? Thank you

Thanks a lot. That was very helpful. Good point about the min "useful" speed as well.

Hello, I've been told that the minimum speed I can run my HVAC fans and pumps at is 20Hz or 1/3 speed. Often cited is the need for "motor cooling". I've looked and can't seem to find manufacturer's reccomendations for motor minimum speeds. These are variable torque loads, not constant torqu...

Thanks a lot, that was what I had thought but wanted confirmation. The motor in question is protected by time delay fuses (picture attached). Does that change anything?

In a building I manage I experienced a situation where a motor failed and tripped the GFI protection on the main switchgear taking down the whole building. I'm not an electrician or an electrical engineer and I want to know if it is common practice to provide GFI protection in a switchgear with...

Hello, I have three natural gas, commercial condensing boilers with forced draft burners. The stack terminates aproximately 30 feet above the boilers. They are experienceing too much draft and are cutting out on flame failure. Currently, there is no barometric damper in the breaching to the...

Thanks a lot jraef & DickDV. Your posts helped clear that up a lot for me!

Hello All, My question concerns a particular VFD that, as indicated in the manufacturer's literature, is rated for a maximum current of 31 amps when used in a constant torque application or 48 amps when used in a variable torque application. Can someone please explain why the large difference...