You can select the field total_refunded_shipping_set.shop_money.amount to export the total refunded shipping amount in the shop currency (including refunded taxes).

If you need a breakdown of the refunded amount before taxes and the refunded tax amount, you can select the following shipping refund order adjustments fields instead (note that these values are negative):

• refunds.order_adjustments.shipping_refund.total_amount - The total amount refunded for shipping (excludes taxes).
• refunds.order_adjustments.shipping_refund.total_tax_amount - The total tax amount refunded for shipping.