Thermally driven heat pumps need three different circuits, two of them provide the machine with the energies that let it work, and the other one reject it closing the energy balance. All three circuits have to be controlled at the same time, taking into account that, except for some cases, the temperature levels of the energy (both supply and demand) vary. Overall control is indispensable if the maximum energy yields are wanted be reached.

In some cases the generator depends very much on the variability of the sun, or the amount of waste energy that can be used. Therefore the design of a system to store exceeding free energies, mitigating thus the fluctuations, is essential and also auxiliary power requirements must be evaluated to assure a constant energy to drive the machine.

Similar considerations have to be done also for the other two energy circuits. There is, however, an extra variable to be taken account of: depending on the final elements and the relation of sensible and latent load the fluid must be sent to the demanding zones or applications with different temperature levels that maintain the satisfaction of the users keeping the thermal/electrical yield of all the facility as high as possible:

For cooling applications, the fluid of the evaporator will be sent to a — usually variable — demand application while the absorber and condenser must be cooled with a heat rejection system.

For heating applications, the varying demand is connected to the medium temperature level (absorber and condenser) and the evaporator must provide with energy at low temperature level. With the — possibly “free” — driving energy in the generator circuit this low temperature energy can be lifted up to the temperature level needed, saving primary energy.

Since only little practical experience with thermally driven heat pumps for heating and cooling applications is available to date, it is necessary to monitor demonstration projects as case studies, providing information on performance under every day conditions and yields of the control strategies implemented on them. At the end of the task the documentation and evaluation of existing projects will help us to show and teach in a real way what kind of things can and cannot be done with TDHP’s depending on the applications.

Also, because of this lack of installed systems where new things can be tested, it is necessary to have simulation programs with trustable results. A list of the available software and a comparison among them must be produced.