Assessing heating and cooling demands of closed greenhouse systems in a cold climate

Reducing greenhouse gas emissions by providing non‐fossil fuel energy sources is imminently necessary. The area of particular interest in this paper is the agricultural greenhouse industry. In these structures, significant heating demands are present, especially in cold climates, and are typically met by combusting fossil fuels. In an effort towards a sustainable energy supply, the potential of closed greenhouse systems in a cold climate is explored. In these systems, natural ventilation for cooling and dehumidification is replaced with active systems, and the thermal energy removed can be re‐used, reducing the overall heating demand. A transient greenhouse model is created using TRNSYS software and validated with natural gas usage data from a reference greenhouse. The annual heating and cooling demands, effect of varying cover materials and potential for heat recovery ventilation are explored for the most concentrated greenhouse areas in Canada. Copyright © 2017 John Wiley & Sons, Ltd.     

Sol-air heating and cooling degree-days

A set of relationships is developed which allow the estimation of sol-air heating and cooling degree-days at any base temperature. The method makes use of existing relationships for hourly utilizability and degree-days, and the only input required is the monthly-average solar radiation and ambient temperature. Solar radiation which is absorbed on outside surfaces and solar radiation which is transmitted through glazings are accounted for in the analysis. Estimated sol-air degree-days are compared with sol-air degree-days determined using longterm hourly data, and good agreement is observed. Sample calculations for a simple structure illustrate the use of sol-air degree days.     

Climate influence on district heating and electricity demands

This paper describes the district heating and electricity load of Kalmar, Sweden. Unfortunately, it has not been possible to examine one full year because the monitoring of the energy use for district heating and electricity, and the outdoor temperature, did not exactly overlap. However, more than 7200 h, of the 8760 in a full year, have been examined. It is shown that the district heat load has a far higher correlation with the outdoor temperature (a coefficient of 0·89), than has the electricity load (0·33). Thus, it is much easier to predict the influence of, e.g. an insulation retrofit for the building stock where district heating is used compared with electricity space heating. It is also shown how an estimate can be made of the thermal transmission factor for the total building stock.     

Modeling of the CSU heating/cooling system

This paper resents a thermal simulation of the Colorado State University solar house. A computer model of the solar energy system was developed and computer runs were made using one year of meteorological data to determine the important design features. The system consists of a flat plate solar collector, main storage tank, service hot water storage tank, auxiliary heater, absorption air conditioner with cooling tower and heat exchangers between the collector and storage, storage and service hot water tank and storage and residence. This system very closely models the CSU house in operating mode one.The results are in the form of monthly integrated values for the pertinent energy quantities. In addition, results are presented which show the effect on the system performance of the collector tilt, collector area and number of covers.     

Recognising the potential for renewable energy heating and cooling

Heating and cooling in the industrial, commercial, and domestic sectors constitute around 40–50% of total global final energy demand. A wide range of renewable energy heating and cooling (REHC) technologies exists but they are presently only used to meet around 2–3% of total world demand (excluding from traditional biomass). Several of these technologies are mature, their markets are growing, and their costs relative to conventional heating and cooling systems continue to decline. However, in most countries, policies developed to encourage the wider deployment of renewable electricity generation, transport biofuels and energy efficiency have over-shadowed policies aimed at REHC technology deployment. This paper, based on the findings of the International Energy Agency publication Renewables for Heating and Cooling—Untapped Potential, outlines the present and future markets and compares the costs of providing heating and cooling services from solar, geothermal and biomass resources. It analyses current policies and experiences and makes recommendations to support enhanced market deployment of REHC technologies to provide greater energy supply security and climate change mitigation. If policies as successfully implemented by the leading countries were to be replicated elsewhere (possibly after modification to better suit local conditions), there would be good potential to significantly increase the share of renewable energy in providing heating and cooling services.     

Greenhouse heating and cooling using aquifer water

An aquifer coupled cavity flow heat exchanger system (ACCFHES) was designed using underground aquifer water for the heating as well as cooling of a composite climatic greenhouse. The performance of ACCFHES was experimentally evaluated for a full winter and a summer season. The ACCFHES makes use of constant temperature aquifer water (24 °C) available at an agricultural field through an irrigation tube well for heating in winter nights and cooling in summer days. The results showed that the average greenhouse room air temperature was maintained 7–9 °C above the outside air during extreme winter nights and 6–7 °C below the outside air in extreme summer days, and temperature fluctuations inside the greenhouse also decreased daily. The average relative humidity (RH) inside the greenhouse also decreased by 10–12% in the winter and increased by more than double in the extreme summer conditions as compared to the outside conditions. A comparison of economic feasibility of the ACCFHES coupled greenhouse was also conducted with conventional greenhouse and open field condition based on the yield of Capsicum annum. The ACCFHES was also compared economically with other existing heating/cooling technologies such as earth-to-air heat exchanger system (EAHES), ground air collector, evaporative cooling using foggers and fan & pad system in terms of net present worth (NPW) and pay back period. It was observed that the NPW of the ACCFHES coupled greenhouse was much higher as compared to the conventional greenhouse and open field condition. The payback period of the ACCFHES coupled greenhouse was the lowest among all other existing heating/cooling systems.     

Sustainable heating and cooling systems for agriculture

Space heating/cooling systems account for approximately 40% of the global energy consumption. Such systems contribute to global warming by emitting 4×10¹⁰ MWh of heat and 3×10¹⁰ tons of CO₂. There is a general understanding that the way to reduce global warming is a more efficient use of energy and increased use of renewable energy in all fields of the society. Ground‐coupled heating/cooling systems, which have proven to make huge contributions in reducing energy consumption in Europe and North America, is here applied for poultry industry in Syria, as an example for the Middle East. There are e.g. 13 000 chicken farms in Syria producing 172 000 tons of meat per year. This industry employs directly almost 150 000 people. The total investments in chicken farming are 130 BSP (2 B€). The annual mean air temperature in Syria is 15–18°C with winter temperatures close to freezing during two months. The chickens need a temperature of 21–35°C, depending on age, and the heating of all Syrian chicken plants consume 173×10³ tons of coal (1196 GWh). In the summer time, the ambient air temperature in Syria could reach above 45°C. The chicken farms have no cooling systems since conventional cooling system is too expensive. The elevated temperature inside the farms reduces the chicken growth and lots of chicken die of overheating. The ground temperature at 10 m depth is roughly equal to the annual mean air temperature. Using the ground as a heat source means a sustainable and less expensive heating of the chicken farms. During the summer, the ground is used as a source for free cooling, i.e. used directly for cooling of the plants without any cooling machines. Current study shows the design and simulated operation of a ground‐coupled heating/cooling system for a typical chicken farm in Syria. Performed national potential study showed that the implementation of such ground coupled heating and cooling systems in the Syrian poultry sector would mean increased poultry production and considerable savings in money, energy, and the environment. Copyright © 2010 John Wiley & Sons, Ltd.     

Review of passive solar heating and cooling technologies

Heating, ventilating, and air-conditioning (HVAC) are parts of the major energy consumption in a building. Conventional heating and cooling systems are having an impact on carbon dioxide emissions, as well as on security of energy supply. In this regard, one of the attempts taken by researchers is the development of solar heating and cooling technologies. The objective of this paper is to review the passive solar technologies for space heating and cooling. The reviews were discussed according to the working mechanisms, i.e. buoyancy and evaporative effects. The advantages, limitations and challenges of the technologies have been highlighted and the future research needs in these areas have also been suggested.     

Simulation of a solar heating and cooling system

This paper presents thermal and economic analyses of a solar heated and air conditioned house in the Albuquerque climate. The system includes the following components: water heating collector, a water storage unit, a service hot water facility, a lithium bromide-water air conditioner (with cooling tower), an auxiliary energy source, and associated controls. The analysis of the thermal performance indicates the dependence of output on collector area (considered as the primary design variable) and shows, for example, the manner in which annual system efficiency decreases as collector area increases. Based on the computed thermal performance, cost estimates are made which show variations in annual cost as functions of collector area and costs of collector and fuel.     

Operational modes of solar heating and cooling systems

This paper emphasizes factors associated with the subsystems that are required to extract heat from solar collectors, store this heat, and deliver it to the loads upon demand. While minimum use of auxiliary energy is the general objective, it must be sought with due regard to safety, convenience and cost. Subsystem alterations that improve energy efficiency typically come at added cost in terms of installation and maintenance. In some cases, the advantages of a specified component or arrangement of components are immediately evident. In other cases, such options are less decisive and will require longer periods of comparative operation to arrive at accurate assessments. The Colorado State University Solar House I allows for such comparative operation in several experimental modes. These selected modes of operation provide for different methods of solar heat transfer and employ different arrangements of system components and control functions. The principles underlying these modes as well as results of these studies are presented. In addition, the methods of operation found necessary for efficient and reliable performance are discussed. While this evaluation is an ongoing process, the initial “start up” and “break in” periods have been experienced and serve as a basis for several recommendations concerning subsystem components and component arrangements.     

Optimal side heating and cooling in a distillation column

One of the effective methods for saving energy in a distillation column is the use of side heating and cooling. This procedure provides the heat supply at a temperature lower than the reboiler temperature and heat removal at a temperature higher than the condenser temperature, both of which are advantageous from the second-law perspective. The purpose of this paper is to demonstrate the effects of side heating and cooling on separation performance. To treat the ideal case, it was assumed that every plate above the feeder plate releases heat with side cooling and every plate below the feeder plate accepts heat by side heating. It is shown that there is an optimum temperature profile based on both the separation performance and second law. The results are presented graphically by the use of an integrated energy-utilization diagram.     

District heating and cooling for business buildings in Madrid

Energy needs for heating and cooling in Spain are of paramount interest in the context of the European roadmap to a decarbonized environment; because of that, it is highly desirable that more examples of district heating and cooling networks are developed. The present work evaluates the implementation of one of them into the climatic environment of Madrid. It consists on a complex of business office buildings with a total useful surface of 50,000 m², linked with heating and cooling rings of 1 km of loop length. Basic energy needs of buildings lead to the following design values: 1.7 MW of electricity, 1.3 MW of heating and 2 MW of cooling. They will be supplied by the trigeneration plant here proposed, which relies on an internal combustion engine.The high demand of cooling for air conditioning makes the dimensioning of the engine critical because of the large differences between the heat demand for summer and the one for winter. If the total amount of the cooling demand is covered with an absorption chiller, the heat demand during the summer reaches about 5 MW. In consequence, a critical decision has to be taken relative to the way the cooling demand is attended: with an absorption chiller (single or double effect) or with a conventional chiller powered by electricity. Applying the criteria developed in the present work, which are focused on maximum primary energy reduction, the fraction of the cooling demand to be met with each technology is determined as a function of the engine nominal power, on the grounds of the instantaneous demand.The high cooling demand during the summer season suggests the inclusion of a thermal solar collector field, to be used for complementing the waste heat rejection from the engine to drive the absorption chiller. During the winter, the heat provided by the solar field could be applied in attending a fraction of the heating demand. Thus a hybrid Trigeneration Plant is introduced. This way, over sizing of the engine can be avoided, as the electric demand is small.The analysis is based on the solution of energy and mass balance equations for a trigeneration plant. Monthly demands and environmental conditions (ambient temperature and solar irradiance) are introduced as input data into the model. Monthly and annual primary energy consumption and CO₂ emission reductions are obtained as outputs. Economical data, such as fuel and operating costs, electricity prices, tariffs and subsidies are considered in order to optimize the size of the plant in terms of its payback period.     

A bottom-up estimation of the heating and cooling demand in European industry

Energy balances are usually aggregated at the level of subsector and energy carrier. While heating and cooling accounts for half the energy demand of the European Union’s 28 member states plus Norway, Switzerland and Iceland (EU28 + 3), currently, there are no end-use balances that match Eurostat’s energy balance for the industrial sector. Here, we present a methodology to disaggregate Eurostat’s energy balance for the industrial sector. Doing so, we add the dimensions of temperature level and end-use. The results show that, although a similar distribution of energy use by temperature level can be observed, there are considerable differences among individual countries. These differences are mainly caused by the countries’ heterogeneous economic structures, highlighting that approaches on a process level yield more differentiated results than those based on subsectors only. We calculate the final heating demand of the EU28 + 3 for industrial processes in 2012 to be 1035, 706 and 228 TWh at the respective temperature levels > 500 °C (e.g. iron and steel production), 100–500 °C (e.g. steam use in chemical industry) and < 100 °C (e.g. food industry); 346 TWh is needed for space heating. In addition, 86 TWh is calculated for the industrial process cooling demand for electricity in EU28 + 3. We estimate additional 12 TWh of electricity demand for industrial space cooling. The results presented here have contributed to policy discussions in the EU (European Commision 2016), and we expect the additional level of detail to be relevant when designing policies regarding fuel dependency, fuel switching and specific technologies (e.g. low-temperature heat applications).     

冷热电联产系统与微型燃气轮机

以发展冷热电联产系统为能源配置方向和以微型燃气轮机为重要发电方式，是第二代能源系统建设的需要，对平衡城市的能源结构、提高能源使用效率、促进环境保护具有现实而长远的意义。文章论述了冷热电联产系统与微型燃气轮机的特点与发展前景。     

Solar district heating and cooling: A review

Both district heating and solar collector systems have been known and implemented for many years. However, the combination of the two, with solar collectors supplying heat to the district heating network, is relatively new, and no comprehensive review of scientific publications on this topic could be found. Thus, this paper summarizes the literature available on solar district heating and presents the state of the art and real experiences in this field. Given the lack of a generally accepted convention on the classification of solar district heating systems, this paper distinguishes centralized and decentralized solar district heating as well as block heating. For the different technologies, the paper describes commonly adopted control strategies, system configurations, types of installation, and integration. Real‐world examples are also given to provide a more detailed insight into how solar thermal technology can be integrated with district heating. Solar thermal technology combined with thermally driven chillers to provide cooling for cooling networks is also included in this paper. In order for a technology to spread successfully, not only technical but also economic issues need to be tackled. Hence, the paper identifies and describes different types of ownership and financing schemes currently used in this field.     

Validation methodology for solar heating and cooling systems

The validation of solar heating and cooling computer programs is still in the early stages of development. Some work has been done in the area but much more is required before a level of confidence can be associated with the use of the programs. A validation methodology is proposed in this report which consists of 4 levels. The first deals with the validation of detailed simulation programs with respect to unmodeled parameters or phenomena. Level 2 addresses the inaccuracies introduced in simplified analysis procedures due to unmodeled parameter variation while level 3 deals with assessment of variation in results due to the field variation of modeled parameters. Level 4 provides a verification of the results of level 3 by comparison studies with field performance data. The result is a quantification of the level of confidence with which the simplified analysis program can be used.To illustrate the Monte Carlo techniques suggested in levels two and three, a case study was prepared. The results from the case study are helpful in appreciating the method proposed and expected results from that method. The validation procedure described in this document will result in the establishment of levels of confidence with which users can predict system performance. The methodology will also assist in the establishment of a meaningful and efficient solar system testing program plan.     

Solar houses/heating and cooling progress report

Performance data on seven solar homes are given. Solar Homes No. 1, 2, 3, and 4 are near Washington, D.C., 39° north latitude, where about half of the winter days are cloudy and temperatures drop far below freezing, sometimes to 0°F. These houses are described in the book Solar Houses and Solar House Models by Harry E. Thomason, published by Edmund Scientific Company, Barrington, New Jersey, 08007. Edmund Scientific Co. also publishes Solar House Plans, for building a house similar to Solar House No. 1, with improvements.

1. Solar House No. 1Solar House No. 1 has been in continuous operation for thirteen years. In its first year, solar heat supplied about 95 per cent of the heat requirements for home temperatures at 70°F, plus or minus 2°F. After 5 yr of operation, the heat collector was rebuilt. Longer-lived materials were used although efficiency was lowered somewhat. Also changes were made in the air conditioning system.

2. Solar House No. 2A number of changes were incorporated in House No. 2, built in 1960 and 1961. Cost for the original system was lowered, but the auxiliary heat cost ran slightly higher. An aluminum reflector was installed at the bottom of the solar heat collector to reflect additional sunlight onto the collector. The air conditioning system in House No. 2 is rather satisfactory, and that type of system is now in House No. 1 as well as in House No. 2.Summertime heat leakage from the solar heat collector into the closet space behind the collector was solved in House No. 2. The closet remains cool. However, at times the temperature in the closet drops too low and a new problem has to be solved by re-introducing heat to the closet.

3. Solar House No. 3The architectural appearance of House No. 3 was improved. Low-cost glazing with a minimum of glass breakage was achieved. The heat collector was moved entirely up to the roof so that winter sunshine enters the living room and built-in swimming pool on the south side. Improved air conditioning was installed.

4. Solar House No. 4A new type of solar heat collector (with asphalt shingles) and a new type of low-cost “Pancake” heat storage were incorporated into this A-frame house.

5. Solar House No. 5House No. 5, planned for a South Carolina firm, was never built due to insufficient funds.

6. Solar House No. 6House No. 6 has been completed in Mexico City, Mexico. The house and system were not constructed as the authors recommended so the solar heating system does not provide the major part of the heat load. Although Mexico City is quite far south (19° north latitude), the temperature drops below the freezing mark at times. (On December 8, 1970, the temperature dropped to 24°F.)

7. Solar House No. 7The authors have designed and engineered a new system, their Solaris “Sunny South Model,” with three principle innovations. (1) The system uses “Pancake” under-the-floor heat storage. (2) The system utilizes a shallow roof-pond solar heat collector with a reflector to intensify solar input. (3) The system allows the warm water from the roof-pond to drain each night to the under-floor “Pancake” heat storage area where it warms the floor and living space. During the summer the roof-pond helps minimize day-night temperature extremes by absorbing excess heat during the day and liberating it at night.

     

The analysis of triangular cycles of cooling and heating

Theoretical study of triangular cycle with cooling and heating at variable temperatures is investigated in this study. Simple approximated correlations for COP are obtained. By implementation of the cooling and heating using multistage machines, single-compressor machines accompanying with refrigerants mixtures, semiconductor thermopiles, and the supercritical cycles with variable temperature of heat rejection, the “triangular” cycle shows promising interesting features.     

Analysis of variable-base heating and cooling degree-days for Turkey

The degree-day method is one of the well-known and the simplest methods used in the Heating, Ventilating and Air-Conditioning industry to estimate heating and cooling energy requirements. In this study, the heating and cooling degree-days for Turkey are determined by using long-term recent measured data. Five different base temperatures ranging from 14 to 22°C are chosen in the calculation of heating degree-days. In the case of cooling degree-days, 6 different base temperatures in the range 18 to 28°C are used. Yearly heating and cooling degree-days are given both in tabular form and as counter maps for all the provinces of Turkey (78 weather stations).