As　a　promising　approach　for　sustainable　development,　the　distributed　energy　system　receives　increasing　attention　worldwide　and　has　become　a　key　topic　explored　by　researchers　in　the　areas　of　building　energy　systems　and　smart　grid.　In　line　with　this　research　trend,　this　paper　presents　a　case　study　of　designing　an　integrated　distributed　energy　system　including　photovoltaics　(PV),　combined　cooling　heating　and　power　(CCHP)　and　electric　and　thermal　energy　storage　for　commercial　buildings　(i.e.,　a　hospital　and　a　large　hotel).　The　subsystems　are　modeled　individually　and　integrated　based　on　a　proposed　control　strategy　to　meet　the　electric　and　thermal　energy　demand　of　a　building.　A　multi-objective　particle　swarm　optimization　(PSO)　is　performed　to　determine　the　optimal　size　of　each　subsystem　with　objectives　to　minimize　carbon　dioxide　emissions　and　payback　period.　The　results　demonstrate　that　the　proposed　method　can　be　effectively　utilized　to　obtain　an　optimized　design　of　distributed　energy　systems　that　can　minimize　environmental　and　economic　impacts　for　different　buildings.