Print Customer's Group Name on the transactional emails

For printing the customer’s group name on the order confirmation email,
Firstly, we need to copy the following file "app/code/core/Mage/Sales/Model/Order.php" to  "app/code/local/Mage/Sales/Model/Order.php" as core files shouldn't be changed.

In Order.php, we should add the following function. This function will return the customer group name.

public function getCustomerGroupName(){
    if ($groupId = $this->getCustomerGroupId()){
        $group = Mage::getModel ('customer/group')->load($groupId);
        if ($group->getId()){
            return $group->getCode();
        }
    }
    return '';
}

Finally, we need to add the following code on the email template to get the group name,
{{htmlescape var=order.getCustomerGroupName()}}

Cheers!!