All of our VAV installation that do not have line voltage at the controller location (VAV box) use the following power supply in a central location. Generally we limit the number of VAV controllers between 4 and 7 per 100VA circuit, depending on the length of wire to the controller and if it has a reheat valve.
I'm not exactly sure what you are referencing...do you mind adding a link to the search or clarifying? I know enough, but I am not going to pretend like I have done this before. Kontrolphreak provided a good explanation about why adding multiple controllers on one transformer might be a bad idea. That is totally the reason I'm asking the questions on this board.
Not what we use for regular installations. But should work for projects such as you have in mind.
Originally Posted by laziboie
I was thinking of one of the small fish tank pumps with a regulator, valve and gauge that I could use to supply pressure to the transducers. I understand the pressure relationship you described, at the moment, I'm not aware of what the psi rating is on a little fish tank pump but I assume it is near 1 psi. I was definitely keeping this in mind though, but a good point to bring up, thanks!
Your idea might work. However I was thinking of a method that'd allow one of your trainees to actually measure flow (at discharge of small duct) and then enter proper correction data into VAV controller.
Small duct, with fan, and installed pitot tube.
Each VAV controller mounted on small board. No particular reason damper actuator has to be mounted on real damper. Plud in power for just THAT controller. Connect tubes to pitot. Start fan ...
You are in operation, for as much as you need to accomplish your goal.
Just my first thoughts. Not worth a thing more than that.
We are going to have a VAV setup with a controller attached and wanted to do exactly like you have described. I'm not sure how feasible it would be to swap out controllers every time we wanted to test a different system. My main concern would be wiring, space and the fact that some controllers have built in actuators while others are separate. Still, definitely going to do this with at least one controller, a small VAV and a fan. Great idea though, thanks![/QUOTE]
Airflow could be generated in a PVC pipe hooked to a small 4" cooling fan like found in a computer, but 120 ac voltage. Add a fan speed control with a knob. Then add a pitot tube flow pickup. Get fancy and add an old inclined watertube gauge that balancers don't use anymore. Setup could be quite small and be used to teach as well as test. Dont forget the yarn on the discharge of the pipe for determining the direction of flow...
You can mount all your devices and xfmr but power up only the set you'll be testing. You could probably use switches or quick disconnects pull aparts. Powering only a few components of a controller will allow you to use a smaller xfmr, maybe a big wal wart transformer?
The way a Control company sizes Transformers for their equipment differs, but here is the BEST Power Supply I can recommend and we use this in Control Panels and for VAV Power feeds.
Typically the VA required for each device at a VAV Box is, 6VA for the Controller, 6VA for the Actuator Motor
, & 6 VA for the Valve, totalling 18VA. Multiply that by 5 = 90 VA & that is how we determine how many Tansformers we need. So for this basic setup, we would use 1 96VA~100VA Transformer for 5 VAV's & add them as needed. There is really no need to buy something at 80%, which ultimately knocks off 1 VAV per Transformer & the reason for this is that there is a Built in Circuit Breaker, which will trip if you cross the power wires on a VAV Controller or have a Controller go Bad.
So, for the sake of Controls & the Engineering of a Control System, bidding work and making sure that your VAV's have sufficient power, these values are all you need to know for VAV's. The Spec Data Sheets for each part will tell you its max operating VA & if there are other power using devices, such as a 2nd Valve Actuator for a Baseboard control valve, then you would obviously do your math Differently and settle with 4 VAV's per 96~100VA Transformer.
These can be purchased from KELE.
The parts # for a 100VA transformer in a box, with a circuit Breaker, receptacle On/Off Switch & LED to let you know that power is present.
The T-PB Series power source provides 24 VAC from a 115 VAC input. Each T-PB Series unit contains an LED that illuminates when the 24 VAC output is operational. An on/off switch is provided in the 115 VAC input. This switch disconnects or connects both the hot and neutral of the input power. A convenience outlet is located on the front panel. This convenience outlet is not controlled by the on/off switch and is always hot. A circuit breaker is incorporated in the 24 VAC circuit, which must be manually reset if the rated 3.0A (Class 2) or 4.0A (Class 1) is exceeded and the breaker operates.The T-PB Series is available in a metal enclosure (UL Listed) for field applications or without the enclosure (UL Recognized) for panel mounting.
T-PB202: 4.0A, 96 VA (Class 1) ,T-PB303: 3.0A, 72 VA (Class 2)
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