Heat Loss Method Research Articles

3D City modeling for urban scale heating energy demand forecasting

An urban energy management tool was developed, which is able to predict the heating energy demand of urban districts and analyze strategies for improving building standards. Building models of different Levels of Detail are investigated and analyzed according to their suitability for forecasting energy demand. Based on the specific 3D city model, an input file is generated, which can be read by the building simulation model. Special focus is put on a method for modeling the heating energy demand of the buildings with the fewest input parameters possible, but one which will give reliable forecast results. A simple transmission heat loss method and an energy-balance method were tested. In both cases, there was a good correlation between the measured and calculated annual values for a case study area of over 700 buildings in Ostfildern, Germany. The results also show that a 3D city model (with low geometrical detail) can be used for energy demand forecasting on an urban scale.

Determination of Clothing Evaporative Resistance on a Sweating Thermal Manikin in an Isothermal Condition: Heat Loss Method or Mass Loss Method?

This paper addresses selection between two calculation options, i.e heat loss option and mass loss option, for thermal manikin measurements on clothing evaporative resistance conducted in an isothermal condition (T(manikin) = T(a) = T(r)). Five vocational clothing ensembles with a thermal insulation range of 1.05-2.58 clo were selected and measured on a sweating thermal manikin 'Tore'. The reasons why the isothermal heat loss method generates a higher evaporative resistance than that of the mass loss method were thoroughly investigated. In addition, an indirect approach was applied to determine the amount of evaporative heat energy taken from the environment. It was found that clothing evaporative resistance values by the heat loss option were 11.2-37.1% greater than those based on the mass loss option. The percentage of evaporative heat loss taken from the environment (H(e,env)) for all test scenarios ranged from 10.9 to 23.8%. The real evaporative cooling efficiency ranged from 0.762 to 0.891, respectively. Furthermore, it is evident that the evaporative heat loss difference introduced by those two options was equal to the heat energy taken from the environment. In order to eliminate the combined effects of dry heat transfer, condensation, and heat pipe on clothing evaporative resistance, it is suggested that manikin measurements on the determination of clothing evaporative resistance should be performed in an isothermal condition. Moreover, the mass loss method should be applied to calculate clothing evaporative resistance. The isothermal heat loss method would appear to overestimate heat stress and thus should be corrected before use.

Effect of posture positions on the evaporative resistance and thermal insulation of clothing

Evaporative resistance and thermal insulation of clothing are important parameters in the design and engineering of thermal environments and functional clothing. Past work on the measurement of evaporative resistance of clothing was, however, limited to the standing posture with or without body motion. Information on the evaporative resistance of clothing when the wearer is in a sedentary or supine posture and how it is related to that when the wearer is in a standing posture is lacking. This paper presents original data on the effect of postures on the evaporative resistance of clothing, thermal insulation and permeability index, based on the measurements under three postures, viz. standing, sedentary and supine, using the sweating fabric manikin-Walter. Regression models are also established to relate the evaporative resistance and thermal insulation of clothing under sedentary and supine postures to those under the standing posture. The study further shows that the apparent evaporated resistances of standing and sedentary postures measured in the non-isothermal condition are much lower than those in the isothermal condition. The apparent evaporative resistances measured using the mass loss method are generally lower than those measured using the heat loss method due to moisture absorption or condensation within clothing. Statement of Relevance: The thermal insulation and evaporative resistance values of clothing ensembles under different postures are essential data for the ergonomics design of thermal environments (e.g. indoors or a vehicle's interior environment) and functional clothing. They are also necessary for the prediction of thermal comfort or duration of exposure in different environmental conditions.

Experimental study of heat transfer characteristics for a refrigerator by using reverse heat loss method

The present study has been carried out to predict the heat transfer characteristics of a residential refrigerator through insulation wall by using reverse heat loss method. The temperature time history characteristics were measured to achieve the steady state condition. In this experiment the steady state condition was reached at about 20 h of heating. The temperature and heat inputs were then averaged with one hour data and considered as the steady state temperature and heat input. From the measured values of temperature and heat input, one can conclude that, the temperature differences between the inside and outside of a refrigerator has a nearly linear relationship with heat input. The overall heat transfer coefficients have been derived by introducing the optimal heat loss function to analyze the heat loss characteristics. The accuracy of heat loss prediction has been checked with various experimental data and the normalized errors of the obtained result are found to be within 2.5%.

A Study on Evaporative Resistances of Two Skins Designed for Thermal Manikin Tore under Different Environmental Conditions

A cotton skin and Gore-Tex skin were designed for thermal manikin Tore to simulate different sweating styles (wet cotton skin inside and Gore-Tex outside to simulate sweating style of thermal manikin Walter, and Gore-Tex skin inside with wet cotton skin outside to simulate sweating style of thermal manikins Newton. The evaporative resistances of two skin combinations with clothing ensembles were compared at two different environmental conditions. In addition, the total evaporative resistance of clothing ensemble was calculated by both heat loss method (option 1) and mass loss method (option 2) according to ASTM F 2370. We found that the effect of different sweating mechanisms on clothing evaporative resistance should be considered. The results showed that the total evaporative resistances obtained by option 2 were more accurate than values by option 1 under an isothermal condition. It was also found that total evaporative resistance differences between two skin combinations with clothing ensembles decreased with increasing clothing ensemble layer. In a non-isothermal condition, the total evaporative resistance calculated by option 1 was more accurate than value obtained by option 2, which was due to lower ambient temperature and condensation between each adjacent layer. (Less)

Empirical prediction method of transmission heat loss in hot water plumbing

A simple approach and practicable prediction method of transmission heat loss would significantly benefit to the comprehensive applications in the hot water system design. This paper proposes an empirical prediction method and defines new parameters to simplify the equation to calculate energy consumption in hot water system. The temperature drop mechanism is established by empirical approach to replace multiple factors in the theoretical heat loss equation developed in air conditional technology. As a result, it is proved that the proposed empirical prediction approximates to the results of theoretical calculation in the range for practical applications.

Radiation loss in the flash method for thermal diffusivity

The boundary radiation heat loss method is investigated for the flash method in measuring thermal diffusivity. Present correction procedures for heat loss are tested experimentally using AXM−5Q (POCO) graphite. In addition, a new method for radiation loss correction is presented based solely on the heating portion of the temperature rise curve. Using the new method, corrections of 35% can be made within a ±3% error. The thermal diffusivity results calculated using the adiabatic expression for various portions of the fractional rise curve and for various heat losses are also presented.

On the Optimalizing Control of Boiler Efficiency by a Heat Loss Method

This paper presents the experimental results and the theoretical analysis of the optimalizing control of boiler efficiency, which is attained by the minimization of the total heat loss consisting of a sensible heat loss of exhaust gas and a heat loss due to CO. The experiment is carried out using a gas-fired boiler. The control method and the experimental apparatus are explained in brief. The experiment shows the optimalizing control is satisfactroy. On the basis of the above results, a mathematical model of the controlled system is constructed, where the input is the excess air ratio and the output the total heat loss. The analysis of the optimalizing control system is performed on the steady-state deviation from the optimum and the stability near the value, taking account of dynamic lags and unsymmetrical characteristics of the system. The contributions of each parameter of the system to these problems are clarified. Moreover, the effect of noise on the steady-state deviation is analysed by use of the probability density function obtained from the Fokker-Planck equation. The theoretical values are found to be in good agreement with the results obtained from the simulation on a digital computer.

On the Optimizing Control of Boiler Efficiency by a Heat Loss Method

On the Optimizing Control of Boiler Efficiency by a Heat Loss Method

Efficiency Determination of Marine Boilers: Input-Output Versus Heat-Loss Method

At the Naval Boiler and Turbine Laboratory boiler efficiencies are determined simultaneously by the input-output and heat-loss methods. This paper discusses the procedures followed in testing boilers for efficiency and the results and relative merits of the two methods. Naval boilers are described as well as the instrumentation and weigh systems utilized in efficiency determinations. Results from over 200 tests performed on some 35 boilers are used as the basis for comparison between input-output and heat-loss efficiency.

Latent heat of fusion

Sodium acetate trihydrate is a phase change material that can be used for long term heat storage in solar heating systems because of its relatively high heat of fusion, a melting temperature of 58 °C and its ability to supercool stable. In practical applications sodium acetate trihydrate tend to suffer from phase separation which is the phenomenon where anhydrous salt settles to the bottom over time. This happens especially in supercooled state. The heat released from the crystallization of supercooled sodium acetate trihydrate with phase separation will be lower than the heat released from sodium acetate trihydrate without phase separation. Possible ways of avoiding or reducing the problem of phase separation were investigated. A wide variety of composites of sodium acetate trihydrate with additives including extra water, thickening agents, solid and liquid polymers have been experimentally investigated by a simple heat loss method. The aim was to find compositions of maximum heat released from the crystallization of supercooled sodium acetate trihydrate samples at ambient temperature. It was found that samples of sodium acetate trihydrate with 0.5–2% (wt.%) Carboxy-Methyl Cellulose, 0.3–0.5 % (wt.%) Xanthan Gum or 1–2% (wt.%) of some solid or liquid polymers as additives had significantly higher heat contents compared to samples of sodium acetate trihydrate suffering from phase separation.