I'm trying to calculate how many zone valves I can put through a 40va transformer.
If I take the zone valve motor amp rating and multiply by 24 volts, divide that total into 40, that's the answer (right)?
Now I'm looking at a honeywell zone valve and it reads the following:
24vac 50 va pilot duty
120vac 4.4 amps full load
28.4 amps lock rotor.
Which number do I use?
zone valve are you using. The numbers you posted seem like relay numbers not Honeywell ZV's. If memory serves me Honeywell ZV's use about .2 amps so you can use 5 of them with a 40 VA transformer.
If you are using a NEMA rated class II standard DC20-92 transformer you can exceed rating up to 200%.
Would you be so kind as to show me how you calculated that? Or tell me what I'm doing wrong. The .2 amps is a 5th of an amp; 24 volts divided by 5 is almost 5, so each zone valve is drawing 5 va; 40 va divided by 5 va is 8 zone valves. There's probably a de-rating in there somewhere?
literature for their zone valves states 5 ZV,s per 40 VA transformer.
They also have a white paper they put out about 10 years ago that states that a 40 VA transformer can be run at 200% of capacity with only a small drop in voltage. This is how we can run three Taco ZV's with a 40 VA transformer as long as it is NEMA rated standard DC20-92 ClassII.For Taco which draws about 1 amp the math would be 1 x 24 = 24 VA per valve x 3 = 72 VA.
With the Honeywell ZV's at .2 x24 = 4.8 divided into a 50 VA = 10.416666 so I would imagine 8 to 10 would be okay with a 50 VA.