Put value to array

Can somebody build the codeigniter querry from this:

Code:

$sql = "SELECT estimated_sum FROM burndown_snap WHERE project_id='$sum1' AND name='$sum2'";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        $burn_actual = "" . $row["estimated_sum"]. ",";
        echo $burn_actual;
}
}

Or something similar that I could list the values from the database.