Dynamic Modeling of Microclimate and Environmental Control Strategies in a Greenhouse Coupled With a Heat Pump System

Abstract

The purpose of this study was to develop and validate a dynamic simulation model to be employed in accurate prediction of microclimate in a greenhouse as a function of dynamic environmental factors. The model has options to evaluate the effects of location, time of the year, orientation, single and double polyethylene glazings, conventional and heat pump heating and cooling systems, open and confined greenhouse systems, CO 2 enrichment, variable shading, and the use of night curtains. Conventional gas furnace and evaporative cooling, respectively, provided heating and cooling in the conventional system. In the heat pump systems, gas-fired heat pump units provided both heating and cooling. The heat pump systems were operated both as an open and a completely confined system. Outputs of the simula tion model included both temporal and vertical distribution of air, leaf, floor and cover temperatures, CO 2 , relative humidity, solar radiation, and photosynthetically active radiation in addition to the dynamics of photosynthesis, respiration, transpira tion, energy and CO 2 use and fixation. Comparison of experimental and predicted results showed that the compared microclimatological parameters were in fairly good agreement. The greenhouse model developed in this study is useful for ecologists, plant scientists, and engineers to evaluate individual or combined effects of various forcing functions on the enclosed environment and plant responses; and to develop control strategies for different parameters. INTRODUCTIONAccurate prediction models for greenhouse and plant growth performance can be used as a design tool and in economic feasibility analyses as well. A dynamic analysis is required for more accurate prediction and control of greenhouse thermal environments. In addition to experimental tests, efforts have been made to predict the greenhouse environment under both steady state and transient conditions. Some reported work on greenhouse models and thermal performance tests include the work of Chandra et al. (1981), Glaub and Trezek (1981), Kindelan (1980), Navas et al. (1998), Pita andVargues (1998), andRijsdijk and Hauter (1993). The purpose of this study was to develop and validate a dynamic simulation model to be employed in accurate prediction of greenhouse energy and moisture exchanges as a function of dynamic environmental factors such as solar energy, outside temperatures and moisture levels, plant moisture and energy exchanges and heat removal or storage. This article deals with the model development, validation and preliminary simulation results.

Simulated Effects of Various Environmental Management Practices on Energy Consumption in Open and Confined Greenhouse Systems

“…Table 1 shows the greenhouse and the crop characteristics used in this study. Yildiz and Stombaugh (2006) reported the theoretical approach, model validation, and all the other greenhouse and crop characteristics. The heat pumps evaluated for open (OHP) and confined (CHP) greenhouse systems were 3-ton (based on system heat removal capacity) gas fired units, and to provide multiposition proportional control it was assumed that 3 units were used in each greenhouse.…”

“…A dynamic simulation model was developed and validated to provide an accurate prediction of greenhouse energy and moisture exchanges as a function of dynamic environmental factors (Yildiz and Stombaugh, 2006). This model was used to predict heating and cooling loads, and to evaluate the operational strategies associated with heating and cooling using the proposed heat pump and a conventional system.…”

“…These systems involve complex tradeoffs between initial and operating costs for cooling and heating, plant responses to various environmental factors and the strategies used to regulate temperature, humidity and CO 2 levels in the crop canopy. Special attention must also be given to the operational strategies associated with the use of heat pumps, especially in maintaining acceptable relative humidity levels within greenhouses.A dynamic simulation model was developed and validated to provide an accurate prediction of greenhouse energy and moisture exchanges as a function of dynamic environmental factors (Yildiz and Stombaugh, 2006). This model was used to predict heating and cooling loads, and to evaluate the operational strategies associated with heating and cooling using the proposed heat pump and a conventional system.…”

Simulated Performance of a Renewable Energy Technology - Heat Pump Systems in Semi-Arid California Greenhouses

“…A dynamic simulation model was developed and validated to provide an accurate prediction of greenhouse energy and moisture exchanges as a function of dynamic environmental factors (Yildiz and Stombaugh, 2006a). This model was used to predict heating and cooling loads, water use, and to evaluate the operational strategies associated with heating and cooling using the proposed heat pump and a conventional system.…”

Simulated Effects of Dynamic Row Spacing on Energy and Water Conservation in Semi-Arid Central California Greenhouses

“…Increased fruit yield in narrow spacings result from greater crop biomass generated by the effect of increased light interception and canopy photosynthesis. A dynamic simulation model was developed and validated to provide an accurate prediction of greenhouse energy and moisture exchanges as a function of dynamic environmental factors (Yildiz and Stombaugh, 2006). This model was used to predict energy and water consumption using different (dynamic) row spacings, plant heights and leaf dimensions.…”