Small Power Conditioners

Astounding that in 2nd decade of the 21st century that commercial controllers can lose their setup memory during power loss. Unfortunately, I don't know of a 24Vac back-up.

Gee, that sounds stupid. What does JC have to say about it?

You could start with a 24 VDD bus which has to be really common. e.g. http://www.trcelectronics.com/Meanwell/ups-module.shtml

That might be enough for 10 units, running all the wires back to a single controller.

There are fire alarm panels that can distribute the 8A as protected Class 2 circuits. e.g. http://cctvpowersupplies.com/power-supplies/12-24-dc-power-supplies/altronix-al300ulxpd16cb-12vdc-or-24vdc-at-2-5-amp-115vac-input-ac-and-battery-monitoring-sixteen-16-ptc-protected-class-2-rated-power-limited-outputs-grey-enclosure-15-5-h-x-12-w-x-4-5-d-ul-listed-ul29.html . I did use a similar one. The charger was built into the panel too and extra battery boxes were available too. Trouble circuits are also there.

Here is a 24 VDC to 24 VAC inverter, but it's only 40 W and they might be coming from here; http://www.powerstream.com/inv-24vdc-24vac.htm which is the same company with the inverter in development.

Here is a 24 VA UPS: http://www.altronix.com/products/data_sheets/DSRESERV1.pdf

here is a wierd idea. Get yourself a standard UPS and then a AC/DC Load. e.g. http://www.calinst.com/products/CSW/CSW_Specifications.htm Now distribute everything back as a class 2 circuit, meaning fused for 100 VA (I think I'm right here)

So, you can generate the 24 VAC that you need. But keep the room totally locked up or have the factory fix it at 24 VAC.

Yep, you would have to run all of the 24 VAC circuits to a central point. I'd probably make the distribution box use alarm fuses and holders or use a PTC thermister.

Who needs all that when you could get a large 120:24 VAC xformer and a bunch of 4A DIN rail mounted breakers and some terminal strips. Feed the transformer from a nice rack mounted, generator friendly, continuous, sine wave output UPS mounted on the wall.

Size the 24 VAC lengths appropriately for voltage drop and run Class 2 wiring.

When I think, I sometimes come up with bizarre solutions at first. Then they trigger better ones.

You might also have less repairs this way.

Here is a 24 VAC @ 3A distribution panel. : http://www.alarmsaf.com/pdf/data_sheets/52-335.pdf

Why not contact Johnson controls and see if they have a capacitor or battery back up for the ECU memory. You needn't power the HVAC system just keep the memory valid and the system will restart when power is restored.

Why not install one 24 vdc emergency battery pack minus the lights in each building. That should keep the logic going for quite a while.

The OP wants 100 VA, 24 VAC not DC

Both have issues, 24 VAC isn't readily available and 100 VA is the maximum for class 2 wiring and 24 VAC distribution systems (even UL approved) don't go to 100 VA for some odd reason. Fused is less than PTC protected outputs.

Can you run 2 ports to the HVAC unit? Don't know?

So, there could be considerable wiring expense and resistive losses to go to a central distribution system.

The general use for HVAC is 24 VAC at 40 VA.

Yep, the op stated ac. I apparently missed that one. Still, A common 24 vac supply can do the job per building. Fire alarm systems do this all the time.