cant seem to find the 90degree discharge on ASHRAE 62.1, but there is one on ASHRAE 90.1-2016 for difference on supply temperature to room temperature.
Technically it is not a rule for 90 degree max SAT, but rather 15 above space temp. Most spaces seem to average a 72 degree heating setpoint so that comes to 87 max supply air and because most of us like to think about even numbers, we end up with 90. In ASHRAE 62.1-2019 look at section 6.2.1.2 for Zone Distribution Effectiveness. The Ez calculation uses 0.8 multiplier for "Ceiling supply of warm air 15°F (8°C) or more above space temperature and ceiling return," which mathematically increases your minimum OA ventilation by 25% from what it should be.
Would reduced airflow across the dx coil, when the boxes close, cause possible flood back at the compressors? Is there additional sensors on the ddc to monitor suction temp/pressure?
Each VAV box controller is set with a minimum and maximum CFM that it can modulated between. The sum of the minimum CFM settings for all of the VAV boxes must add up to the minimum CFM required by the AHU or RTU.
If you are the design engineer, you can determine that by the pressure your fan will be generating and the pressure drop of the devices it is pushing air thru, including coils, elbows, adapters, etc. If you are the installer, you can run the system, and use a manometer to sample a locations in the duct.
How do you check if the amount of air being delivered is enough? Do they size the max by air changes per hour or l x w x 1.2? I have heard both please help!
No, sizing is not by air changed per hour. Nor is it by room dimensions. Although both of those are part of the overall calculations. The design engineer does a heat gain calculation (aka a load calc) for that zone adding up all the sensible and latent heat sources (walls, windows, computers, etc) on a "peak design" climatic day to determine how many BTU/h need to be removed from the space. This is almost always done with software and no one calculates by hand anymore. Then assuming a 55F supply air temp, uses that temp and the required BTU/h to calculate the required CFM of air needed.
@@anthonyrodriguez243 Automation classes are generally very specific to the brand of controllers, and even their vintage. At our offices in the Chicago and Milwaukee area, we train Carrier commercial controls dealers on the Carrier OPEN BACnet system. The Level 1 class meets one day per week for 7 weeks. The next one is in Melrose Park, IL and starts in October. The Carrier factory has similar classes in the Atlanta area and sometimes Syracuse.
VAV, by definition, is a cooling only system at the air handler level (other than a brief morning warm-up). Does your VAV zone box have its own local zone heater such as electric resistance or hot water coil, separate from the main air handler?
@@timothyrichardson8567 To be clear, to heat the VAV zone you are talking about that specific VAV zone needs its own local heater separate from the morning warm-up heater that is in the main air handler and shared with all zones. So you need an electric heater instead the VAV box or on the baseboard permitter of that zone.
We don't use GE products at our office. Plus PTACs are pretty straightfoward... they all have the same dimensions and they just plug into the wall. No one services them anymore either... the hotel just swaps them out if they fail.
If you start being politically correct, I will stop watching your videos. 1:20 Basics 1:50 Multi Zone System 12:35 VAV Breakdown 1:18:30 VAV Rules 29:02 Zone Layout 43:35 Minimum Outside Air Question 47:50 Inlet Guide Vanes 52:40 Affinity Laws 1:03:30 Compressor Capacities 1:11:40 Hot Gas By Pass 1:50:00 Digital Scroll 1:25:54 Energy Savings 1:30:00 VAV types Also, if you have motors (fans) that are rated for higher Hz, then it's fine to run it's VFD at higher Hz.
