5VA power supply can only output about 200mA current at 24VAC, it’s rather small. You can try but typical 24VAC sprinkler solenoid draws about 200mA already, and it needs additional to power the RPi, so I feel this power supply is underpowered.
However, one work-around you can use is to additionally use a microUSB cable connected to a USB adapter to power RPi directly. This way RPi will draw power from the USB adapter, while 24VAC only needs to power the sprinkler solenoid. To avoid the two power supplies competing with each other, here is what I suggest that you do:
1. on the orange terminal block, take out the wire that’s closer to the COM green terminal block, and keep the other wire in as before.
2. take out the common (COM) wire, and connect it directly with the wire removed from step 1 above.
3. plug in 24VAC (now only one wire remains in the orange terminal block), and also plug in a microUSB cable to power RPi.
This way, the two power supplies won’t compete with each other.