Renato Lazzarin

Chemical dehumidification by liquid desiccants: theory and experiment

Chemical dehumidification of air by a liquid desiccant in a packed tower has been investigated both theoretically and experimentally for air conditioning and industrial applications. A computer model of a packed tower, able to determine heat and mass transfer between air and desiccant, has been developed and a parametrical study was carried out considering the solutions H2O/LiBr and H2O/CaCl2 to determine the optimum operative conditions. An experimental apparatus including a packed tower and a desiccant regenerator has been described together with experimental results: a set of 70 experimental runs with H2O/LiBr. Data have been reported and compared against the results of the computer code simulations.

Technical and economical analysis of heat recovery in building ventilation systems

Abstract Heat recovery in ventilation systems can be obtained from both the sensible fraction and the latent fraction. The possible sensible and total heat recovery depends on the climate and on the operating period. Total heat recovery is limited in winter by the humidity of the supply air; this lowers the exchange capacity in the heating period. Three different climates are considered (Milan, Rome, Palermo), evaluating the recovery for unitary air ventilation flow rate and the economic savings, also taking into account the reduction in the heating or cooling capacity. Heat recovery in a ventilating system must always be evaluated, since the investment is often profitable.

Ammonia-water absorption machines for refrigeration: theoretical and real performances

Abstract In principle, absorption chillers of the ammonia-water type could work at temperatures well below the usual air-conditioning temperatures, arriving at the range 250–260 K, which can be useful for refrigeration applications. This possibility is studied for an air-cooled machine, comparing the results with the experimental data supplied by a manufacturer that recently commercialized such a refrigerator. The prediction is fair, and the study allows an insight into the internal parameters and into the possible behaviour for more severe conditions than those studied.

An open cycle absorption heat pump

Abstract The absorption cycle can be also of the open type. This concept has been utilized in developing solar cooling absorption systems. Another possibility not yet investigated is an open cycle absorption heat pump. The system rests upon the utilization of a packed tower operating with liquid desiccants. The tower dehumidifies both the exhausted air of heating plant and the exhaust of a natural gas boiler. A conventional heater heats up the regenerator of the sorbent and the inlet air. Simulations give a PER of the system (the open cycle heat pump) higher than 1.3 with respect to the Gross Calorific Value of natural gas. This value is difficult to obtain with the more complex closed cycle absorption or vapour compression cycle motor driven heat pump.

Steady and transient behaviour of LiBr absorption chillers of low capacity

Resume Two, low capacity, LiBr, absorption chillers (4.5 and 25 kW) expressly designed for solar cooling have been tested. The manufacturers performance curves have been checked, then the investigation was extended to different values of the main parameters. Transient behaviour has been examined. For solar cooling duties it was found that control by simple on-off cycling is unacceptable owing to the large resulting energy loss. Two alternative control strategies are suggested together with the appropriate plant schemes.

Comparison of heat recovery systems in public indoor swimming pools

The heating of swimming pools can be expensive in terms of energy costs and energy-saving measures which are much more effective than the simple recovery of the exhausted air are recommended. A new open-cycle absorption system is presented here, operating by chemical dehumidification on the exhausted air. It allows important energy savings of the same order as the motor-driven heat pump systems, although its technology is in principle simpler and cheaper.

Two years of operation of a large solar cooling plant

Abstract A solar plant was installed with a surface area of 440 m2 of evacuated-tube collectors, a reflecting surface of the same area and an absorption refrigeration system for air-conditioning the CERIT building of Pordenone. A 43 m3 heat-storage unit, at temperatures of 80–90°C, and a 150 m3 cold-storage unit were also installed. These components form the largest solar cooling plant in Europe. After two years of operation, it is possible to evaluate the project as a whole, and to appreciate the contribution of the flat solar reflector and the working of the absorption unit.

Performance analysis of heating plants equipped with condensing boilers

Abstract The behaviour of the condensing boilers is strictly bound to the temperatures of the water coming back from the plant. This temperature depends on the control modes and on the meteorological conditions. The seasonal performance has been computed for a heating plant of a building equipped with a condensing boiler simulating the load at short time intervals through a suitable modification of TRNSYS. The study has been carried out in the climate of Padova. For other towns a rough estimate is proposed.

Theoretical analysis of an open-cycle absorption heating and cooling system

Abstract In warm countries, such as Italy and Spain, the increasing demand for space conditioning cannot be met by the current capacity of installed electric power. This has led to a growing interest in cooling with natural gas. An interesting thermal cooling system uses open-cycle absorption. It treats the air directly without heat exchangers and with very low temperature drops. With absorption dehumidification it is possible not only to obtain a cooling system similar in performance to conventional thermal cooling systems, but also, with few modifications, a high-performance heating system fed by a natural gas burner, which combines simplicity with PER typical of a gas driven heat pump. The proposed new system described in the paper is studied both in winter and summer mode, evaluating the influence of the different parameters.

A new HVAC system based on cogeneration by an i.c. engine

A new HVAC system is proposed and studied. The plant is equipped with a reciprocating i.c. gas engine which produces electric energy with heat recovery from the jacket water heat and the exhaust. The electric energy serves the lighting and emf for the building and individual room reversible air-water heat pumps that mainly satisfy sensible cooling and a fraction of the winter heating load. An open-cycle absorption system, which treats the primary air, meets the summer latent load and year round ventilation requirements. In winter, the system operates as an open-cycle heat pump. The regeneration of the sorbent is obtained by the i.c. engine heat recovery. The proposed system is analysed by comparing its performance with a traditional plant, both in summer and winter mode.