Fan Coil Unit Research Articles

Failure Analysis of a Corroded Threaded Fitting in an Ammonia Refrigeration System

A corroded threaded fitting on a direct-expansion ammonia fan-coil unit was found to be leaking in a refrigerated food-handling warehouse. Efforts to stop the leak by tightening the threaded connection resulted in the failure of the male fitting, causing a catastrophic release of ammonia refrigerant. Subsequent analysis of the subject threaded connection found that the threads of the male carbon steel fitting were severely deteriorated by atmospheric corrosion. The installation location of the subject fan-coil unit was such that it repeatedly experienced significant condensation and frost accumulation and, therefore, needed to be regularly defrosted. It was this combination of repeated condensation/frost accumulation and a cyclic freeze/thaw process which resulted in the accelerated atmospheric corrosion of the subject threaded connection.

Multi-variable Optimization of HVAC System Using a Genetic Algorithm

Geothermal is a fast-growing alternative heat source for HVAC systems due to higher energy efficiency than conventional heating and cooling systems. However, the initial cost of using a ground source HVAC system is higher compared to an air source system. Studies about system design and operation are necessary to reduce the initial cost and ensure that the ground source heat pump system has high efficiency, resulting in a lower total life-time cost. In this study, a multi-variable evolutionary computation algorithm is proposed for generating optimal parameters for a geothermal source HVAC system. The system consists of borehole heat exchangers (BHE), a water-to-water heat pump and a fan coil unit (FCU) and it was modeled and simulated using MATLAB. The design parameters were calculated by minimizing the energy consumption. These parameters include cold water supply temperature, FCU air flow rate and cooling water flow rate for the underground heat exchangers. In addition, based on an experimental building, a case study was presented. Using this model, the optimal set points were calculated and used as a designed system. Energy consumption of this system was reduced by about 10% compared to the system operated with a fixed supply cold water temperature (7°C). Furthermore, the relationship between system energy consumption and heat pump capacity was expressed. The result showed that the energy consumption increased due to decrease in PLR when the capacity is increased.

Decision making of HVAC system using Bayesian Markov chain Monte Carlo method

Building simulation has become an indispensable decision making tool since it is capable of capturing dynamic behavior of building systems and predicting impact of energy saving components. However, it has been well acknowledged that simulation prediction is often significantly influenced by treatment of uncertain inputs. This paper presents multi-criteria (construction cost, total energy consumption) decision making of HVAC systems under uncertainty. In this study, a library building was selected and modeled using EnergyPlus 6.0. There were two HVAC candidates: (1) variable air volume (VAV) for interior zone+fan coil unit (FCU) for perimeter zone+gas boiler+electric chiller, (2) VAV+FCU+gas boiler+electric chiller+ice thermal storage system. For uncertainty analysis, unknown inputs were identified based on the literature and the Latin hypercube sampling (LHS) method was employed. Then, Bayesian decision theory was applied to solve stochastic decision making. In particular, the paper includes preferences of building stakeholders (three architects, four simulation experts, three HVAC experts) by using Markov chain Monte Carlo (MCMC). It is shown that such quantitative stochastic appraisal yields more meaningful information than the traditional deterministic approach, and helps to improve confidence in simulation results.

Radiant Cooling with Dehumidified Air Ventilation for Thermal Comfort in Buildings in Tropical Climate

Radiant cooling is an alternative air-conditioning that havs been implemented successfully in high latitude regions. In tropical region as Thailand, radiant cooling is quite challenge due to its cooling performance being limited by high-moisture ambient air. This paper reports an investigation of radiant cooling in a tropical building. The study comprises full-scale experiments of a radiant cooling system with cool panels installed in a room of a laboratory building. A separate fan coil unit was installed to remove humidity of the ventilation air before suppluying it into the room. A software namely TRNSYS was used to model the systems in order to determine the heat extraction rate of the cool panels. Thermal comfort level in the room was evaluated by predicted mean vote (PMV) index. The results show that the radiant cooling is able to use for air conditioning for human comfort in tropical buildings. However, a sophistical system to control temperature of the chilled water supplied to the cool panels and the fan coil unit for the ventilation air dehumidification is inevitably required.

A Central Air Conditioning System Design for Hotel in Guangzhou

The primary mission of this design is the air conditioning design of a hotel in Guangzhou city. The calculation of cooling load & heat load, division of the air conditioning system and the determination of the scheme, the design of the duct and water system, and the design of the smoke prevention and extraction system are all included. According to the related standard and considering the energy saving and comfort requirements, the air conditioning system are determined through the economic and technological comparison. Primary return air system is used for open office area and dining hall; fan-coil units with fresh air system is adopted for the guest rooms of the hotel; and the VRV system is adopted for the large conference room. The new air in restaurant rooms and the large conference room is handled by full-heat type fresh air exchanger; new air in guest room is handled by air conditioning units.

Thermal-environment characteristics and comfort of combined radiant-floor (Korean heating system ondol) and convective cooling system

The thermal-environment characteristics of the existing forced-convection cooling system were compared with those of the convective cooling system, which combined the radiant-floor cooling system using floor-heating panel typically applied to apartments in South Korea with the forced-convection cooling system using improved fan coil unit. The subjective warm/cool-feeling responses to the combined radiant-floor and convective cooling system in the questionnaire survey conducted among the test subjects were analyzed to establish the basic data for the combined cooling system. The results show that in the thermal-equilibrium condition, the vertical air temperature difference in the model living room is larger in the forced-convection-cooling condition. Most of the subjects feel a proper warm/cool feeling on their entire body, but they feel colder on the foot and lower body in the combined-cooling condition.

Evaluation of terminal coupling and its effect on the total delta-T of chilled water systems with fan coil units

Most chilled water circulation systems with fan coil units suffer from a low temperature differential between the supplied and returned water. On-site investigation shows that the relationship between total cooling consumption and total water flow rate of real systems is different from that of single coil units mainly as a result of the interaction of the terminals. When certain terminals close their water valves, the other terminals have higher water flow rates and lower water delta-T values. This study presents a quantitative analysis of terminal coupling and its effect on system characteristics. System coupling factor is used as an indicator to describe the total degree of fan coil unit coupling in a system. To observe the effect of the system coupling factor, a dynamic simulation platform is constructed and simulation tests are performed. The results show that the higher the system coupling factor is, the larger is the total delta-T loss under partial load conditions. Based on this indicator, certain problems of system design can be reviewed from the perspective of terminal coupling.

Heating Effect by Using An Electricity-Powered Hot Water Heater and Fan Coil Unit in Greenhouse

Heating Effect by Using An Electricity-Powered Hot Water Heater and Fan Coil Unit in Greenhouse

Experimental validation of a theoretical model for a direct-expansion solar-assisted heat pump applied to heating

This paper discusses the experimental validation of a theoretical model that determines the operating parameters of a DXSAHP (direct-expansion solar-assisted heat pump) applied to heating. For this application, the model took into account the variable condensing temperature, and it was developed from the following environmental variables: outdoor temperature, solar radiation and wind. The experimental data were obtained from a prototype installed at the University Carlos III, which is located south of Madrid. The prototype uses a solar collector with a total area of 5.6 m2, a compressor with a rated capacity of 1100 W, a thermostatic expansion valve and fan-coil units as indoor terminals. The monitoring results were analyzed for several typical days in the climatic zone where the machine was located to understand the equipment's seasonal behavior. The experimental coefficient of the performance varies between 1.9 and 2.7, and the equipment behavior in extreme outdoor conditions has also been known to determine the thermal demand that can be compensated for.

직달일사를 이용한 잠열축열식 바닥난방 시스템이 냉방부하에 미치는 영향에 대한 검토

In this research, the effect of a heating system, which is powered by direct solar energy accumulated in phase change material (PCM) as heat storage material installed on the floor surface, on the cooling load was studied. Cooling load of a test building designed for this research was measured with fan coil unit and factors affecting it were also estimated. Experiments were performed with and without PCM installed on the building floor to understand the effect of the PCM on the cooling load. Additionally, to confirm the experiments results, the prediction calculation formula by average outside temperature and integrated solar radiation was composed using multivariate regression model. The results suggested that the heating system with PCM on the floor surface has the potential to shift electric power peak by radiating heat, stored during the daytime in it, at night, not increasing the total cooling load much.

Thermoeconomic analysis of ground-source heat pump systems

SUMMARY A thermoeconomic analysis of a ground-source heat pump (GSHP) system with a vertical or horizontal ground heat exchanger, a type of heat delivery system, was performed using the modified productive structure analysis method. In this analysis, the unit cost of geothermal heat delivered to a room using GSHP system was estimated. The unit cost of heat delivered was calculated to be $0.063/kWh for input of electricity with a unit cost of $0.140/kWh for a GSHP with a coefficient of performance (COP) of 3.27. Exergy destruction and monetary losses due to the irreversibility that occurs at each component of the system were also estimated. The unit cost of heat was found to be inversely proportional to the COP of the heat pump and proportional to the electricity input. The greatest monetary loss occurs in the geothermal heat exchanger in which considerable mass of brine flows in long pipes and in the fan-coil unit which features a complex configuration of pipes in the air passages, respectively. Copyright © 2013 John Wiley & Sons, Ltd.

Energy-efficient HVAC systems: Simulation–empirical modelling and gradient optimization

Abstract This paper addresses the energy saving problem of air-cooled central cooling plant systems using the model-based gradient projection optimization method. Theoretical–empirical system models including mechanistic relations between components are developed for operating variables of the system. Experimental data are collected to model an actual air-cooled mini chiller equipped with a ducted fan-coil unit of an office building located in hot and dry climate conditions. Both inputs and outputs are known and measured from field monitoring in one summer month. The development and algorithm resulting from the gradient projection, implemented on a transient simulation software package, are incorporated to solve the minimization problem of energy consumption and predict the system's optimal set-points under transient conditions. The chilled water temperature, supply air temperature and refrigerant mass flow rate are calculated based on the cooling load and ambient dry-bulb temperature profiles by using the proposed approach. The integrated simulation tool is validated by using a wide range of experimentally collected data from the chiller in operation. Simulation results are provided to show possibility of significant energy savings and comfort enhancement using the proposed strategy.

Energy and exergy analysis of a solar-assisted heat pump space heating system for clear days

The studies over solar–assisted heat pump systems have been performed mostly on time periods when solar radiation is high. Therefore, this study focuses on performance analysis of a solar–assisted heat pump system which stores the energy during the clear day and uses it as a heat source of heat pump space heating system during the night. Energy and exergy analyses divided into two parts, which are the analyses of solar water heating system (SWHS) and water source heat pump space heating system (WSHPSHS). As a result, the exergy efficiencies of the heat pump unit and WSHPSHS were 84.9% and 79.5%, respectively while the corresponding COP values were 2.95 and 2.68. Also, the exergy efficiency of the SWHS was obtained to be 7.28%. The greatest irreversibility occurs in evaporator, fan–coil unit and solar collector for the heat pump unit, WSHPSHS and SWHS, respectively.

Analysis on Load-Undertaking of Fan Coil Unit with Fresh Air System

The paper analyses some common handling processes on the dedicated outdoor air system with conventional fan-coil units in summer, and studies undertaking cooling loads and humidity loads separately.

Calculation methods for a complete air conditioning study

PurposeThe purpose of this paper is to describe and categorize calculation methods for conducting a complete air conditioning study. More specifically, this paper is a general review of cooling loads calculation methods, psychrometric calculations for installing a central air conditioning unit, ways of fan coil units connection and air duct calculation methods.Design/methodology/approachThis paper was based on two pillars: a dissertation for an industrial facility and technical information found after methodical research.FindingsAfter a brief reference of the calculation methods and the air conditioning systems installed in this industrial facility, this paper concludes with the most appropriate calculation methods for this industrial facility.Research limitations/implicationsThis study describes some calculation methods. Thus, future research could be addressed toward the analysis of more methods.Practical implicationsThis paper includes implications for choosing the most appropriate calculation method according to the air conditioning system installed.Originality/valueThe originality of this paper lies in the fact that, except for the theoretical part, there are some examples taken from a case study, thus it can be used as a future guide for selecting methods and systems of industrial air conditioning.

Modeling and Simulation of Chilled Water System for Central Air Conditioning

Considering the central air conditioning system is highly susceptible to interferences from external environment, this paper established a dynamic mathematical model for chilled water system with the air conditioning area, fan coil unit and air conditioning area interference factors. Selection of chilled water system as a controlled object, designed the energy saving control system for central air-conditioning. The inputs of PID controller are deviation of actual temperature and setting temperature, and the change rate of the deviation; output is operation frequency of pump. Experiment shows that, PID control system in 90% time operating at a frequency of 10Hz-40Hz, average is 32.5Hz. Compared with no control system, the pump power consumption was reduced 33.9%.In conclusion, PID control in the central air conditioning system have a good energy saving effect.

A Central Air Conditioning System Design for Guesthouse in Changsha City

This article presents the design of the air conditioning system in the building. In the project, ice storage for cold source and electric boiler thermal storage for heat source are taken while variable primary flow is used for water system. Taking into account the functions of each part, all air and fan coil unit with fresh air system are applied in ventilation system. The design of air exhaust system is introduced. A detail scheme about the annual operational regulation for energy saving is proposed. During the designing process, energy conservation is given enough attention, and the reliability of operation is also ensured.

Experimental analysis of a solar absorption system with interior energy storage

This study examines experimentally the cooling application of a solar absorption system with interior energy storage that uses two different auxiliary systems. The experiments were performed at Uludag University, Bursa, Turkey on the 3rd and 4th of August 2010 that had the approximately same average outdoor temperature, 31°C. A solar hot water was delivered via a 40 m2 array of flat plate solar collectors that drove a lithium chloride (LiCl) absorption heat pump with a cooling power peak of 20 kW. A solar-powered air conditioning system was designed for heating and cooling in a test room that had a total floor space of 30 m2. Chilled water produced in the evaporator was supplied to the fan coil units, and the heat of condensation and absorption was rejected by means of a wet cooling tower. An electric heater and an air source heat pump were used as auxiliary systems for the absorption cooling application for two different cases when the solar energy was insufficient. Temperature variations were recorded for the absorption machine components, the test room, and the outdoors. The cooling energy, thermal energy, and daily average coefficient of performance (COP) of the absorption system were calculated for two days. Solar absorption cooling was considered for two different auxiliary systems and is presented in this manuscript. The results showed that the daily average COP of the absorption system was 0.283 for Case 1 and 0.282 for Case 2. For both cases, the interior energy storage of the absorption system enabled it to satisfy the cooling demand during the night while solar energy was not available.

Linking HVAC type and student achievement

Research has long-linked HVAC system type to room noise levels, and it has long-linked room noise levels to student learning. Uninformed design decisions and the absence of policy combine with ineffective execution and insufficient enforcement to produce noisy mechanical systems for schools. Some school HVAC systems place both fans and compressors in the classroom itself, as part of DX units; others utilize remote compressors as part of chillers, but in-room fan motors as part of fan coil units; still other systems use remote AHUs and remote chillers so that neither compressor nor fan motor is exposed to the classroom. This pilot study intends to search for a broader link between HVAC system type and student achievement exams in elementary schools.

Heating and Cooling System for Utilization of Surplus Air Thermal Energy in Greenhouse and its Control Logic

Purpose: Utilizing air thermal energy during over-heated time in the greenhouse is a necessary component to save greenhouse heating costs for nighttime. However, there is no practical way to implement the related principles. Methods: In this study, a heating and cooling system which utilizes the surplus air thermal energy in a greenhouse was developed. Available air thermal energy and heating load for this experimental glasshouse were estimated based on temperature conditions of the plant growth and weather data. Results: Estimated values were 400 MJ/day for maximum surplus air thermal energy and 340 MJ/day for maximum heating energy which were target values of the design as well. The system consists of a heat pump, fan-coil units and heat storage tanks which are divided into low and high temperature tanks. Moreover, a new control logic was developed for surplus air thermal energy utilization. Conclusions: This paper explains the details of conceptual design process of the system. Results of test operations showed that the developed system performed the recovery and supply of the thermal energy according to design purposes.