You guys are complicating too much. Its not sum of buy and sell beacuse buy for 1 person is sell for other. 24H VOLUME IS SUM ON ALL TRANSACTIONS.
Like this here on binance. It dasnt matter if its green or red in here. If it was created by stoploss or take profit or any other poo poo. Just add amount of every transaction and you have volume.
Volume is sum of all transactions not circulated amount of bitcoin. Thats why volume can be higher than marketcap - i've seen coin beeing pumped 1000% which 1 day volume was 10 times bigger than marketcap (every coin change hand 10 times during 1 day). And with 1 btc you can create 10 000 btc fake volume buing and selling to yorself. (thats how shit exchanges are becoming popular (lbank, uex or bitforex) - boosting trading volume trading with themselve)
"It supposed to be 1000 BTC since only 1000 BTC circulating."
It would be too hard to track each btc to know that this transaction has btc that was calculated in other transaction these day.
A coin with a good and almost equal number volume of being bought and sold is an indication of healthy coin.
Wrong !
Every coin has equal number of volume being bought and sold. When you buy on market someone else have to sell. Thats how it works.