During the work in IEA Task 25 also a Type 107 has been developed for TRNSYS-15 [5]. The source code has now been updated to TRNSYS-16. To avoid conflicts the Type number has been changed to 177. The Type uses the method of characteristic equations [4], which can be used to describe the part load behaviour of ad — and absorption chillers. For application of this method to single stage absorption chillers the four mean external temperatures at the heat exchangers (Generator, Absorber, Condenser, Evaporator) are combined in one parameter (ДД) using the Duhring coefficient B to take the applied working pair into account. For common operating conditions of H2O/LiBr chillers B can be set constant in a range of 1.1 to 1.2.

ДД ttG — tA —{tc — t E )•B (3)

With the characteristic temperature difference (ДД0 the cooling capacity QE can be described as a linear function, if the variation of all heat transfer coefficients (which are combined in the slope sE) is negligible and if the imperfection of the internal heat recovery as well as additional losses (which are both described by rE) are constant or proportional to the load (or ДД, respectively).

Qe — Se •ДДt + Ге (4)

Commonly these assumptions of linearity are fulfilled in a wide part load range and the capacity of an absorption chiller can be characterised by (4) with an accuracy of ~10%. A linear part load behaviour is also to be expected, when a modified characteristic temperature difference ДДї* is used, where the more often available inlet and outlet temperatures are used.

ДД t*:— ta — (1 + B)• tAC + B • tE (5)

In addition, the accuracy can be improved [6], if the characteristic parameters are not set constant but are allowed to vary as function of the external temperature lift (AtACE = tAC — tE).

QX — SX (^ACE )^ДД t + rx (^ACE ) (6)

Since there are three capacity equations (X = G, E, AC) twelve parameters have to be determined by linear interpolation e. g. of test measurement data under stationary operating conditions as have been prepared by ILK. The determination of the characteristic parameters sX and rX from these values will be described in the following section.