Well here is a little tip that saved me a lot of health and ammo. Go through the revolving door, run forward a bit until the templars start shoot at you. Then run back into the revolving door and wait on the other side (outside the lab). The templars will follow you and each one will go through the revolving door. Once they go through the revolving door, blast away. They will not know what hit them. After one Templar goes through and you kill him, the next one will go through the revolving door. Kill him, and then the next Templar will go through...etc. If no more templars follow you but you can still see them (green dots on the radar) on the rader then go through the revolving door and get them to shoot at you and then go back through the revolving door and wait for them to go through the revolving door.... It takes patients but in the long run you won't lose health and you can conserve a lot of ammo instead of running in and blasting.....

Templars are pretty dumb if you catch them off guard as I did in the above method.