Controlling the consumption profile of office buildings can be used to provide balancing services to the power grid at a financial benefit without violating its thermal comfort constraints. The economic advantage of such a service is a reduction in the total operating cost, but also an increase in average occupants’ comfort when using our control scheme. We study these effects for the case of participating in the secondary frequency control market of Switzerland. Moreover, we examine the advantages of engaging in the intraday energy market. We propose a method for solving the flexibility bidding problem for a building in order to partake in the ancillary services market. The proposed solution is based on the combination of a new intraday control policy and two-stage stochastic programming. We also study the sensitivity of this economic benefit to electricity pricing. Our findings are based on extensive simulations with real data for energy prices, ancillary service bids, meteorological records and the frequency control signals for the year 2014 as transmitted by Swissgrid.