ASERCOM Energy Efficiency Award 2006

Innovative developments for energy saving in the field of refrigeration, heat pumps and air conditioning, that promise to be successfully marketed, can candidate for the ASERCOM Award.

The 2006 price winning company is the Swedish Bubble Expansion Valve BXV(R)AB, for an innovative expansion device, affecting a better overall refrigerant heat transfer in the evaporator, and thus a better system efficiency.

In small and medium sized refrigeration units, a dry expansion system, controlled by a thermostatic valve, is common practice. This system requires that the vapour leaves the evaporator in a superheated state. Thus part of the evaporator is used to attain a dry, superheated condition, and this deteriorates the overall heat transfer of this component. This drawback is not found with flooded evaporators, in large industrial applications. In these types of systems more liquid refrigerant is supplied to the evaporator than is evaporated in one pass. The surplus of liquid, not evaporated at the outlet, is re-circulated. These so called liquid overfeed of flooded systems show an excellent refrigerant side behaviour of the evaporator because the entire surface is for boiling heat transfer. Expansion of the liquid refrigerant in the industrial capacities is controlled by a float valve, preventing that liquid accumulates in the condenser, thus keeping the condenser internally empty.

The awarded invention aims to extend the liquid overfeed system to small equipment as well. The expansion (throttling) is controlled by a valve, which position is derived from the condition of no liquid level in the condenser, similar to the float valve system described above. The new device allows that liquid together with a small amount of gas leaves the condenser. This non condensed gas ‘slip stream’, which of course must be low, is measured and this acts as a signal for the expansion valve. The new device incorporates an ejector to get a good fluid recirculation in the evaporator loop, a tiny drum to separate flash gas and a unit to return oil to the compressor, heated by sub cooling of the liquid from the condenser. All these functions are integrated into a compact unit. In the control no electronics are found. Beside the advantage for the evaporation the new device allows for a good performance of the condenser (no liquid build up), which pressure can go along with the seasonal and daily air temperature (floating pressure).

The energy savings depend on the type of equipment and whether or not electronic thermostatic expansion devices are used in the systems to compare with. However energy savings between 10 and 20% might be attained. In the light of this energetic profit and the anticipated costs for the system it is expected that the new system can, in several applications, compete successfully with the traditional dry expansion equipment with superheating controls.