Fundamentals of „Design Guide I“

The Design Guide offers the most important tips for the design of energy efficient buildings (rooms) in the early phase of planning. They shall help to optimize the design for a given climate in a best way. The EDG I does on purpose not give any information about the remaining need for heating or cooling, but it shows how minimize them an appropriate design. The EDG I is based on the following scientific insights: It has been shown the temperature of room under the influence of the climate alone, the so-called “free-run-temperature” to depend only on two key parameters: The “thermal inertia” characterized by the time constant tau (in h), respecting the storage capacity of the room as well as its loss-factor. It shows how fast a room reacts to changes in its environment: weather. The “solar temperature correction” gamma or “the gain-to-loss ratio”. It shows how much the influence of the external air-temperature is compensated for by the irradiation across the transparent elements, as windows. It respects the so-called “solar gains” only as far as they are usable within the comfort-limits set for the internal temperature, as for example 20 to 26°C. Whenever the
“free-run-temperature”(FRT) stays within the comfort limits, no heating or cooling is necessary: “Zero-Energy-Hours” (ZEH). Counting the number of ZEH of a room over a year, then the room with the most ZEH will be the best adapted to the climate. Presenting the ZEH as a function of gamma and tau: “Climate Diagram” shows what values for gamma and tau yield the most ZEH, e.g. the best adapted, most energy-efficient room. The table: “Climate Characterization” gives a first insight in such values: The best values for gamma and tau for a given climate for the main directions: North/South and East/West for an operation without internal sources and also with internal sources of 40 W/m2, switched on from 0800 am to 0500 pm. In addition the sensitivity to deviations from these best values are indicated, The number of the maximum attainable number of ZEH is given, The influence of a variable sun-shading device: no device, internal sun shading, external device is also given. To arrive at architecturally important values: light/heavy structure, glazing dimension and glass quality, the further properties of a room have to be considered: U-values and size of the opaque parts, air-infiltration (leakage), room volume must be taken into account. This is done in the diagrams under “Glass-Area”. The values of

U-value and area of the opaque external walls of the room,
Room volume,
Air infiltration (leakage) as estimated air-change rate,
Floor area,
Combination of U-value and solar energy-transmission g (=0.87*SHG-coefficient) can be taken from a table of currently available glazings but also new combinations can be created.

Three diagrams lead to concrete values for the so defined room:

A first diagram “Glass Area” shows how the best gamma-values from the tables can be attained with the choice of glazing partition and glazing quality, here the architect selects the size of the glazing and its quality in a way still keeping the best value of gamma,
A second diagram “Loss Factor” shows the resulting overall loss-factor of the room, relevant for the power- and energy need,
The third “Structure” diagram shows the resulting time constant tau. This value should still be within the range of best tau indicated in the table.

If this value is not near to the best value of tau, one starts again with diagram one (changing amount and quality of glazing) until both best values gamma and tau are satisfactorily attained. These conditions have to be interpreted within the sensibility range indicated in the table. To enable the user to an even better optimization, the curves ZEH(gamma,tau) are collected in the diagrams “Optimization”. There all curves of ZEH(gamma,tau) as well as the heating hours HH(gamma,tau)(number of hours where the FRT is below the comfort limit) and cooling hours CH(gamm,tau) (number of hours where the FRT is above the comfort limit) are presented. With the aid of these curves the user can himself judge the effect of a deviation from the best values of gamma and tau on ZEH, HH and CH: sensitivity. It also shows, how many heating and/or cooling hours are related to the maximum of the ZEH and for example how one could avoid any cooling or heating hours by a suitable compromise in the choice of gamma and tau. Graphic: Left field: Climate data / Zero-energy-hours / Best Values of gamma, tau / Sensitivity Right feld: Architecture / Glazing Area / Structure / Insulation Level Diagram 1: best Glazing Quality: UG, g-value, Glass Area Diagram 2: Resulting loss factor K / if several possibilities for UG/g: select the one with smallest loss factor K Diagram 3: Resulting Time Constant tau Bottom feld: Comparison with best values from table / optimization: if ok: end; if correction necessary: go back to top: architecture.