The most significant decisions about low energy design are made early in the design process. Passive measures such as orientation, glazing, shading, thermal mass, airtightness and ventilation options are easier to incorporate at the early stages.
Similarly, active measures such as energy efficient ventilation with heat recovery do require space to be allocated for them, and it is always less painful to allocate space early.
There are always opportunities to save energy by careful selection of environmental system at any stage of the design. We will always look at the long term cost / benefit and include maintenance and lifecycle as part of the appraisal.
David Frank is a CIBSE registered Low Carbon Consultant
David Frank Consulting, 2 All Saints Close, St Ives, Cambridgeshire, PE27 3SZ