Assigning to variable dynamic item state based on other variable

Hi,
I tried to find how to solve my problem but I’m fail.

Rule like below works ok:

var Number temperature = (JAD_11.state as DecimalType)
sendCommand(Termostat_jadalnia,temperature.toString)

but If I want to generate state dynamically based on other variable and item - it fails

var Number hours = now.getHour
var Number temperature = ("JAD_" + hours + ".state") as DecimalType
sendCommand(Termostat_jadalnia,temperature.toString)

I have tried many combinations of (), “” and always have error

ie
Could not cast JAD_8.state to org.openhab.core.library.types.DecimalType