It could be nice to use the real head stress you have in your tropical region. First control all management practices and/ or housing deficiencies that induce heat stress, then if it persists you can go ahead with new approaches.
Redimo's response above is excellent. If additional heat stress is required after following his suggestion, you can reduce air exchange rate to increase heat inside the building where the broilers are kept. You will need to monitor ammonia concentration as you reduce air exchange though. Please be very careful as you modify ventilation because small changes can have large effects on temperature and the welfare of the birds.
Reduce water intake. Provide higher energy ration than usually given. Adjust air flow . Increase the density of birds housed /provide less space per bird. Lighting routine adjustment will help also.