In this paper is investigated the ability of multi-energy systems (MESs) in acquiring resources from energy markets to supply the demand and supporting System Operators (Trans-mission/Distribution) by providing flexibility. The participation of MESs in multiple markets represents an opportunity and it is expected that market rules are designed to ease their involvement.

The paper offers an overview of the simulations of a MES participating in multiple markets. The MES acquires resources for supplying the demand in the (very) short term (i.e., the day-ahead and intra-day) on energy markets, where acts as balance responsible party (BRP).

On energy markets the MES purchases the cheapest resources to supply the demand and sells the pro-duction excesses at the highest prices. Furthermore, the MES participates in flexibility markets to increase its revenue and of-fer a support to system operators facing safety and reliability issues.

A co-optimization Mixed Integer Linear Programming endowed with a flexibility model was implemented to carry on the simulations of participation in multi-markets and the eco-nomic indicator was adopted for the assessment phase. A district heating system operating in the Milan area was adopted as real MES to be simulated.