The estimated working set memory comming from write operations (TCHD is the entire working set estimate).
Yoy can find the description here: http://pubs.vmware.com/vsphere-50/index.jsp?topic=%2Fcom.vmware.vsphere.monitoring.doc_50%2FGUID-4B6BD1C0-AA99-47F1-93EF-4921D56AE175.html
Regards
Bjørn Hansen