Displacement ventilation has been successfully applied for more than twenty years in Europe and it represents an opportunity for China.

Displacement ventilation (DV) is based on vertical stratification of temperature in the occupied zone of rooms. Buoyancy flows generated by heat sources govern the air distribution in rooms with DV. If properly designed DV has potential to provide higher ventilation effectiveness, i.e. better inhaled air quality for occupants and lower energy consumption than mixing ventilation.

In order to avoid thermal discomfort due to draughts and vertical temperature difference, the temperature distribution should be carefully predicted in the design stage. The REHVA and ASHRAE methods to design displacement ventilation systems for thermal comfort are introduced in this paper and critically reviewed.

The scientific literature shows that the temperature, indoor air quality and venti¬lation, noise and light, and the possibility to control them individually does affect human performance. For cost-benefit analysis it is not sufficient to have information demonstrating a statistically-significant effect of the indoor environmental quality on health and work performance, the dose response relationship of the effect must be quantified. For the temperature, ventilation and indoor air quality was it possible to develop the quantitative relationships describing their effects on office work or sick leave. These relationships have a high level of uncertainty. However, using them is preferable to the current practice of ignoring the effects on health and performance when designing buildings and selecting building operation practices because they have a high economical impact. Usually an increment of 1% of productivity may offset the yearly energy costs. The full costs of installation and running the building can be offset by productivity gains of just under 10%. The pay-back time for investments to improve indoor environmental quality is generally below 2 years.

The main aim of this paper is to present the Italian translation of the REHVA guidebook about indoor climate and productivity in offices in order to attract the attention of building owners, employees, employers and building designers on the effects of indoor environment on office work.

Improving energy efficiency in the Heating Ventilation and Air conditioning (HVAC) systems in buildings is critical to achieve the energy reduction in the building sector, which consumes 41% of all primary energy produced in the United States, and was responsible for nearly half of U.S. CO2 emissions. Based on a report by the New Building Institute (NBI), when HVAC systems are used, about half of the zero net energy (ZNE) buildings report using a radiant cooling/heating system, often in conjunction with ground source heat pumps. Radiant systems differ from air systems in the main heat transfer mechanism used to remove heat from a space, and in their control characteristics when responding to changes in control signals and room thermal conditions. This dissertation investigates three related design and control topics: cooling load calculations, cooling capacity estimation, and control for the heavyweight radiant systems. These three issues are fundamental to the development of accurate design/modeling tools, relevant performance testing methods, and ultimately the realization of the potential energy benefits of radiant systems.

Cooling load calculations are a crucial step in designing any HVAC system. In the current standards, cooling load is defined and calculated independent of HVAC system type. In this dissertation, I present research evidence that sensible zone cooling loads for radiant systems are different from cooling loads for traditional air systems. Energy simulations, in EnergyPlus, and laboratory experiments were conducted to investigate the heat transfer dynamics in spaces conditioned by radiant and air systems. The results show that the magnitude of the cooling load difference between the two systems ranges from 7-85%, and radiant systems remove heat faster than air systems. For the experimental tested conditions, 75-82% of total heat gain was removed by radiant system during the period when the heater (simulating the heat gain) was on, while for air system, 61-63% were removed. From a heat transfer perspective, the differences are mainly because the chilled surfaces directly remove part of the radiant heat gains from a zone, thereby bypassing the time-delay effect caused by the interaction of radiant heat gain with non-active thermal mass in air systems. The major conclusions based on these findings are: 1) there are important limitations in the definition of cooling load for a mixing air system described in Chapter 18 of ASHRAE Handbook of Fundamentals when applied to radiant systems; 2) due to the obvious mismatch between how radiant heat transfer is handled in traditional cooling load calculation methods compared to its central role in radiant cooling systems, this dissertation provides improvements for the current cooling load calculation method based on the Heat Balance procedure. The Radiant Time Series method is not appropriate for radiant system applications. The findings also directly apply to the selection of space heat transfer modeling algorithms that are part of all energy modeling software.

Cooling capacity estimation is another critical step in a design project. The above mentioned findings and a review of the existing methods indicates that current radiant system cooling capacity estimation methods fail to take into account incident shortwave radiation generated by solar and lighting in the calculation process. This causes a significant underestimation (up to 150% for some instances) of floor cooling capacity when solar load is dominant. Building performance simulations were conducted to verify this hypothesis and quantify the impacts of solar for different design scenarios. A new simplified method was proposed to improve the predictability of the method described in ISO 11855 when solar radiation is present.

The dissertation also compares the energy and comfort benefits of the model-based predictive control (MPC) method with a fine-tuned heuristic control method when applied to a heavyweight embedded surface system. A first order dynamic model of a radiant slab system was developed for implementation in model predictive controllers. A calibrated EnergyPlus model of a typical office building in California was used as a testbed for the comparison. The results indicated that MPC is able to reduce the cooling tower energy consumption by 55% and pumping power consumption by 26%, while maintaining equivalent or even better thermal comfort conditions.

In summary, the dissertation work has: (1) provided clear evidence that the fundamental heat transfer mechanisms differ between radiant and air systems. These findings have important implications for the development of accurate and reliable design and energy simulation tools; (2) developed practical design methods and guidance to aid practicing engineers who are designing radiant systems; and (3) outlined future research and design tools need to advance the state-of-knowledge and design and operating guidelines for radiant systems.

La letteratura scientifica evidenzia che la temperatura, la qualità dell’aria interna, la ventilazione, il rumore, la luce e la possibilità di controllare questi parametri individualmente influenzano le prestazioni umane. Per l’analisi dei costi-benefici degli edifici non è sufficiente avere dei dati che dimostrano l’influenza della qualità dell’ambiente interno sulla salute e sulle prestazioni lavorative, è necessario quantificarla. Per la temperatura e per la qualità dell’aria interna è stato possibile sviluppare relazioni quantitative circa i loro effetti. Le relazioni presentate hanno un elevato grado d’incertezza. Comunque, quando si progettano gli edifici e si scelgono le modalità operative è meglio utilizzare queste relazioni che ignorarne gli effetti sulla salute e sulle prestazioni poiché questi hanno un forte impatto economico. Un incremento dell’1% delle prestazioni lavorative può compensare completamente i costi annuali energetici. Gli interi costi di installazione ed esercizio di un impianto di condizionamento in un edificio possono essere compensati con un incremento della produttività del 10%. Usualmente il tempo di ritorno di un investimento per migliorare la qualità dell’ambiente interno è inferiore a due anni.

L’obiettivo principale di questo lavoro è quello di presentare la traduzione della guida REHVA dedicata all’influenza del clima interno sulle prestazioni lavorative al fine di promuovere nei proprietari degli edifici, nei datori di lavoro, negli occupanti degli edifici e nei progettisti italiani la consapevolezza su questo argomento

In this study the influence of the personalized supply air temperature control strategy on energy consumption and the energy-saving potentials of a personalized ventilation system have been investigated by means of simulations with IDA-ICE software. GenOpt software was used to determine the optimal supply air temperature. The simulated office room was located in a cold climate. The results reveal that the supply air temperature control strategy has a marked influence on energy consumption. The energy consumption with personalized ventilation may increase substantially (in the range: 61-268%) compared to mixing ventilation alone if energy-saving strategies are not applied. The results show that the best supply air temperature control strategy is to provide air constantly at 20°C. The most effective way of saving energy with personalized ventilation is to extend the upper room operative temperature limit (saving up to 60% compared to the reference case). However, this energy-saving strategy can be recommended only in a working environment where the occupants spend most of their time at their workstation. Reducing the airflow rate does not always imply a reduction of energy consumption. Supplying the personalized air only when the occupant is at the desk is not an effective energy-saving strategy.

In passato la ragione principale per l’utilizzo dei filtri era la protezione delle macchine per il trattamento dell’aria. Tuttavia negli ultimi anni, grazie allo sviluppo di una ampia letteratura scientifica, è stato riconosciuto che lo scopo principale della filtrazione dell’aria è la protezione della salute delle persone. Un elevato numero di studi dimostra che i filtri possono diventare sorgenti inquinanti. In questo primo articolo si descrivono le possibili cause del fenomeno e le soluzioni ingegneristiche oggi disponibili. Sul prossimo numero torneremo sull’argomento

Impatti, adattamento e vulnerabilità Le cause e le responsabilità dei cambiamenti climatici sono state trattate sul numero di ottobre della rivista Cda. Approfondiamo l’argomento presentando il documento: “Cambiamenti climatici 2007: impatti, adattamento e vulnerabilità” votato ad aprile 2007 dal secondo gruppo di lavoro del Comitato Intergovernativo sui Cambiamenti Climatici (Intergovernmental Panel on Climate Change). Si tratta del secondo di tre documenti che compongono il quarto rapporto sui cambiamenti climatici.

Politiche, misure e strumenti per contenere le emissioni di CO2 Illustriamo l’ultimo contributo al quarto Rapporto sui cambiamenti climatici votato a maggio 2007 dal terzo gruppo di lavoro del Comitato intergovernativo “Intergovernmental Panel on Climate Change”.

Il Rapporto affronta la problematica delle tendenze delle emissioni dei gas serra e il tema della mitigazione a breve e lungo termine. Presentiamo un’analisi critica delle proposte del documento.