It seems you don't know the heat capacity of your kiln. As a rule thumb, you can use the following procedure to determine your start temperature: Cold start the kiln with a full load of wet lumber, run a heating phase as you normally would, eg. open heat valves to max, introduce steam spray/humidification and keep all vents 100% closed for the first 4 hours. Note the DB temperature. The max DB temp you can reach at this stage is a good guide temperature to use throughout. If you cant reach the DB after drying has commenced, reduce the DB setpoint by 1 Deg C until it can be maintained and set your desired EMC/RH with your WB setpoint. In an energy starved system, you will see that you can reach higher temps when the lumber MC goes below ±20%.