iRTG incorporates urban agriculture into and improves energy efficiency in buildings. iRTG concept recycles low-grade, waste thermal energy for growing vegetables. iRTG is an adaptable concept to promotes food security through urban agriculture. Indoor building climate affects iRTG more than outdoor climatic conditions. iRTG achieved annual CO2 and cost savings of 113.8 kg CO2 (eq)/m2/yr and 19.63 €/m2/yr.