Study of Liquid Desiccant Air-Conditioning for High Performance Greenhouses

Greenhouses have become an invaluable source of year-round food production. Further development of viable and efficient high performance greenhouses is important for future food security. Closing the greenhouse envelope from the environment can provide benefits in space heating energy savings, pest control, and CO2 enrichment. This requires the application of a novel air conditioning system to handle the high cooling loads experienced by a greenhouse. Liquid desiccant air-conditioning (LDAC) have been found to provide high latent cooling capacities, which is perfect for the application of a humid greenhouse microclimate. TRNSYS simulations were undertaken to study the feasibility of two liquid desiccant dehumidification systems based on their capacity to control the greenhouse microclimate, and their cooling performance. The base model (B-LDAC) included a natural gas boiler, and two cooling systems for seasonal operation. The second model (HP-LDAC) was a hybrid liquid desiccant-heat pump dehumidification system. The average tCOPdehum and tCOPtotal of the B-LDAC system increased from 0.40 and 0.56 in January to 0.94 and 1.09 in June. Increased load and performance during a sample summer day improved these values to 3.5 and 3.0, respectively. The average eCOPdehum and eCOPtotal values were 1.0 and 1.8 in winter, and 1.7 and 2.1 in summer. The HP-LDAC system produced similar daily performance trends where the annual average eCOPdehum and eCOPtotal values were 1.3 and 1.2, but the sample day saw peaks of 2.4 and 3.2, respectively. The B-LDAC and HP-LDAC results predicted greenhouse temperatures exceeding 30°C for 34% and 17% of the month of July, respectively. Similarly, humidity levels increased in summer months, with a maximum of 14% of the time spent over 80% in May for both models. The percentage of annual savings in space heating energy associated with closing the greenhouse to ventilation was 34%. The additional annual regeneration energy input was reduced by 26% to 526 kWhm-2, with the implementation of a heat recovery ventilator on the regeneration exhaust air. The models also predicted an electrical energy input of 245 kWhm-2 and 305 kWhm-2 for the B-LDAC and HP-LDAC simulations, respectively.

The Influence of Copper Binding on the Stability of the SCO Protein from Bacillus subtilis

Every aerobic organism expresses cytochrome c oxidase to catalyze reduction of molecular oxygen to water, and takes advantage of this energy releasing reaction to produce an electrochemical gradient used in cellular energy production. The protein SCO (Synthesis of cytochrome c oxidase) is a required assembly factor for the oxidase, conserved across many species. SCO is implicated in the assembly of one of two copper centres (ie., CuA) of cytochrome oxidase. The exact mechanism of SCO’s participation in CuA assembly is not known. SCO has been proposed to bind and deliver copper, or alternatively to act in reductive preparation of the CuA site within the oxidase. In this body of work, the strength and stability of Cu(II) binding to Bacillus subtilis SCO is explored via electronic absorption and fluorescence spectroscopies and by calorimetric methods. An equilibrium dissociation constant (Kd) of 3.5x10-12 M was determined as an upper limit for the BsSCO-Cu(II) interaction, via differential scanning calorimetry. In the first reported case for a SCO homolog, dissociation kinetics of Cu(II) from BsSCO were characterized, and found to be dependent on both ionic strength and the presence of free Cu(II) in solution. Further differential scanning calorimetry experiments performed at high ionic strength support a two-step model of BsSCO and Cu(II) binding. The implications of this model for the BsSCO-Cu(II) interaction are presented in relation to the mechanism of interaction between SCO and the CuA site of cytochrome c oxidase.