Similitude for buildings conditioned entirely by ambient energy

While whole-building dynamic simulation programs can accurately predict indoor comfort in buildings conditioned by ambient energy (from the sun, sky, air, and ground), skill and time requirements represent a barrier to their widespread use. Simplified design tools present opportunities to establish targets for building characteristics during the predesign phase that promote desired performance, as well as to guide subsequent design refinements. This study uses a first-order model that includes solar gains, internal heat gains, envelope losses, ventilation cooling, and thermal mass. Similitude variables are solar load ratio SLR , internal heat load ratio ILR , ventilation cooling load ratio VLR and thermal time constant (ratio of thermal capacitance to envelope losses) τ . Heating and cooling season energy balances are approximated by 〈 I L R 〉 + 〈 S L R 〉 = 1 and 〈 I L R 〉 − 〈 V L R 〉 = 1 , respectively, where angle brackets signify temporal averages. Example values necessary to achieve 100% ambient conditioning in sixteen US climate zone are determined. With peak heating losses/cooling gains set to 10 W/m 2 of floor area, and internal heat gains of 3 W/m 2 , January 〈 S L R 〉 ranging from 0.42 to 1 served heating-dominated climates, while annual VLR up to 98 was required for cooling-dominated climates. Seasonal thermal time constants (ratio of dimensional time constant to total time of ambient source/sink insufficiency) were up to 0.83 for heating-dominated climates and as high as 6 for cooling-dominated climates. A benefit of similitude is that a range of building designs with the same values of the similitude parameters will have identical performance. This response is invaluable for adjusting building characteristics during the design process.