State officials plan to use federal economic stimulus funds to make nine prisons more energy efficient.

On Thursday, the State Bond Commission signed off on a financing deal that takes advantage of federal economic stimulus financing to get $31 million in energy-efficiency upgrades for the prisons.

The money would pay for new boilers, chillers and other equipment at prisons across the state.

Department of Corrections Undersecretary Thomas Bickham said the upgrades were needed because many state prisons are aging and relying on old equipment.

But some commission members questioned whether the savings will materialize, as similar deals in the past have left government agencies paying for expensive upgrades, without seeing the savings originally promised.