KRN Heat Exchanger and Refrigeration shares made a bumper debut on stock markets on Thursday, doubling investors' money. The shares were listed at ₹480 on NSE, marking a premium of 118% over its IPO price of ₹220 per share. On BSE, the shares were listed with 114% premium at ₹470. The ₹342-crore IPO was subscribed over 213 times.