ASHRAE Method Research Articles

Influence of degree days calculation methods on the optimum thermal insulation thickness in life-cycle cost analysis for building envelopes in Mediterranean and Semi-Arid climates

The life-cycle cost analysis (LCCA) is one of the most widely used and validated methods to identify the optimum insulation thickness of the building envelope. This method depends on two parameters—heating and cooling degree days (HDD, and CDD). There are various methods for HDD and CDD calculation, the results of which vary significantly depending on the climatic zone. Therefore, this study aimed to analyse the optimum expanded polystyrene insulation thicknesses of a typical wall in Andalusia, Spain, obtained by the LCCA method to demonstrate variations and uncertainties of the results of the LCCA method based on HDD and CDD calculated by the “hourly”, UKMO, and ASHRAE methods, and with different base temperatures in the conditions of Mediterranean and Semi-Arid climates. On average, the HDD values calculated by using the ASHRAE method were lower, by 12.5%, than those calculated using UKMO and the “hourly” method. The CDD values calculated using the ASHRAE method were lower, by 29%, than those obtained using UKMO and the “hourly” method. Consequently, the optimum insulation thicknesses determined based on CDD and HDD calculated using the ASHRAE method were, on average, 14% underestimated compared with the thicknesses obtained using the UKMO and “hourly” methods. The results obtained showed that with an increase in the continentality of the climate, it becomes crucial to correctly use one or another method for calculating degree days to determine the optimum insulation of the building envelope using the LCCA method, which, in turn, requires the development of validation methods.

Comparative Analysis of CIBSE Admittance and ASHRAE Radiant Time Series Cooling Load Models

Due to the impacts of carbon emissions on climate change and the expected dramatic increase in global cooling demand by 2050, it is of a paramount importance that the required energy to cool buildings is accurately predicted. This ensures that equipment is appropriately sized, which ultimately reduces energy consumption and global carbon emissions. CIBSE and ASHRAE standards are both widely adopted for cooling load predictions, but they adopt different calculation methods, with CIBSE adopting admittance and ASHRAE adopting radiant time series (RTS), which produce significantly different results in cooling load. This study comparatively and qualitatively evaluates the CIBSE admittance and ASHRAE RTS cooling load models by analysing their structures and key input parameters for a mock-up building to identify inconsistencies between the two methods. There were flaws within both models that resulted in the CIBSE method underpredicting the cooling load, whereas the ASHRAE method typically overpredicting it. This resulted in a maximal average difference of over 60%. The substantial predicted cooling load difference was mainly caused by the ASHRAE RTS model, which was highly receptive to solar gains, and it consequently led to overprediction in cooling load when compared to the CIBSE admittance model.

Selection of a method for calculating heat gain from solar radiation to determine the load on the climate system of the cabin of a mobile car

Introduction. The article analyzes and selects the most rational methods for calculating the heat gain from solar radiation. The correct calculation of this component of the heat balance allows you to correctly determine the power of the projected cabin climate system, which will ensure optimal working conditions at the workplace of mobile car operators.
 Problem Statement. The objective of this study is to analyze and select a rational method for calculating heat gain from solar radiation for the correct determination of the thermal load on the climate system of the cabin of a mobile car.
 Theoretical Part. To implement the task, the most common methods for calculating solar radiation were described and analyzed in detail and the most accurate ones were recommended.
 Conclusions. The more labor-intensive method of V.N. Bogoslovskiy (taking into account the time of day) can be recommended for automated calculations in Excel, and the method of P.Y. Gamburg (taking into account the sides of the horizon) — for comparative estimated engineering calculations. When conducting "in-depth" model calculations and accounting for solar radiation, the ASHRAE method is explicitly suitable, which has two important advantages: it takes into account the solar factor in relation to a specific type of glazing and is adapted for automated calculations in ANSYS FLUENT.

Performance improvement of a photovoltaic-thermal system using a wavy-strip insert with and without nanofluid

The influence of the wavy-strip insert on photovoltaic-thermal (PVT) system performance was studied. To this end, computational fluid dynamics were used to model the 3-D PVT system and wavy-strip insert. The effect of the wavy-strip insert in a given total mass flow rate was examined on different numbers of the tube (N), which is in the range of 5–25. A rise in N has a direct correlation by an increase in PVT efficiencies; meanwhile, for N > 16 based on the ASHRAE method, heat removal factor and the overall heat-loss coefficient tend to be almost constant. Moreover, the effect of the wavy-strip insert is more pronounced in a lower number of tubes, so that for N = 5, the heat removal factor improved by 18%, and the overall heat-loss coefficient reduced by 3.5%. The PV plate temperature distribution is a crucial issue that can lead to serious thermal stress and lifetime degradation. A detailed study on the PV plate temperature distribution demonstrates that using the wavy-strip insert considerably reduces the temperature gradient. For N = 16, the optimum performance of the PVT module was obtained, and hence the effect of different Reynolds numbers ranging from 600 to 1600 was examined for it. It has been found that the use of insert in considered Reynolds number range will cause the thermal and electrical efficiencies to improve by 6.92–8.64% and 2.01–2.45% compared to a typical PVT system, respectively. In entire cases, the pump power consumption compared to the PV cells’ electrical output power is negligible. A comparative study on the performance improvement of this method and other commonly used methods was carried out. It has shown that this method can become competitive with other methods to improve the PVT performance; meanwhile, it can tackle with substantial problems of previous common methods. Lastly, for optimum configuration of the studied PVT system, further improvement is achieved by dispersing Al2O3 nanoparticles into the working fluid. The results elucidate that the integrated PVT system/Al2O3-water based nanofluid with a wavy-strip compared to the typical PVT system leads to improve electrical and thermal efficiencies by 3.5% and 12.06%, respectively.

The choice of the method for calculating heat supply from solar radiation to determine the load on the climate system of the cabin of a mobile machine

The aim of the study is to analyze and select a rational method for calculating heat suply from solar radiation for the correct determination of the thermal load on the climate system of the cabin of a mobile machine. The correct calculation of this component of the heat balance allows to correctly determine the power of the climate system of the cabin, which ensures optimal working conditions at the workplace of operators of mobile machines. To achieve the goal, the most common methods for calculating solar radiation were described and analyzed in detail, and the most accurate ones were recommended. The more laborious Bogoslovsky method (taking into account the time of the day) can be recommended for automated calculations in Excel, and the Hamburg method (taking into account the horizon sides) – for comparative evaluative engineering calculations. When carrying out “in-depth” model calculations and accounting for solar radiation, the ASHRAE method is explicitly suitable, which has two important advantages: it takes into account the solar factor in relation to a specific type of glazing and is adapted for automated calculations in ANSYS FLUENT.

Techno-economic analysis of ground and air source heat pumps in hot dry climates

The use of ground source heat pump (GSHP) systems in cold climates, such as those in parts of North America, Scandinavian countries and China has been discussed for decades. However, hot and dry climates are encountered in vast regions across the globe but, unfortunately, not much research has taken place in the use of GSHP systems in hot and dry regions. This paper aims to investigate the feasibility of using GSHP systems in hot and dry regions, and Saudi Arabia is an example. This paper introduces for the first time of a techno-economic analysis to evaluate the use of GSHPs compared to the conventional air source heat pump (ASHP) systems in this type of climate.In order to compare the economics of geothermal heat pump systems to other HVAC alternatives, a direct capital cost comparison is made between an example GSHP and ASHP. This is based on the initial investment, payback period, cost energy saving and length of the ground loop, which was calculated for a simple case using the ASHRAE method. Despite the increase in the initial capital costs of GSHP, because of the extra expensive drilling costs for the ground loop heat exchanger and piping the feasibility of GSHP system is worthy of investigates.It is concluded that the GSHP is feasible, albeit with a long payback period, typically 10–20 years, depending on the conditions, setup and predictions. Also it will be seen that there is a savings in CO2 emissions and there may be a substantially decrease in the total costs using GSHP compared to ASHP.

Sensitivity analysis using simulations for a ground source heat pump – implementation on a solar passive house

Having in sight the need for a strong reduction in CO2 emissions and the fluctuation of the price of fossil fuels, the ground source resources alongside with the ground source heat pumps are becoming more and more widespread for meeting the heating/cooling demand of several types of buildings. This article targets to develop the thermal modelling of borehole heat storage systems. Trying to emphasize some certain advantages of a GSHP (ground source heat pump) with vertical boreholes, a case study analysing a residential solar passive house is presented. The numerical results are produced using different modelling software like DesignBuilder, EED (Earth Energy Designer) and a sizing method for the length of the boreholes (ASHRAE method). The idea of sizing the length of boreholes (main design parameter and good index in estimating the system’s cost) using two different methods shows the reliability of this modelling tool. The study shows that borehole’s length of a GSHP system can trigger a difference in electricity consumption up to 22%. Moreover, this sensitivity analysis aims to prove that the design of the whole system can be done beforehand just using modeling tools, without performing tests in-situ.

Analysis on the Influence of Nanoparticles of Alumina, Copper Oxide, and Zirconium Oxide on the Performance of a Flat-Plate Solar Water Heater

In this work, a solar flat-plate collector integrated with four riser tubes having 0.5 m2 area is designed and fabricated. Experiments were conducted using three working nanofluids, namely, alumina, copper oxide, and zirconium oxide, along with the base working fluid water of different weight fractions. The efficiency of collector and storage tank is calculated using the ASHRAE method, and the obtained results were compared. The experimental result shows that alumina nanofluid influences the collector efficiency nearly about 17% for the collector and 13.5% for the storage tank compared to the base working fluid water. The efficiency of the solar collector by appending 0.4% Al2O3, CuO, ZrO2, and water is found to be 55, 51.3, 47, and 38%, respectively. Experimental results raveled that the addition of nanoparticles to water as heat transfer fluid enhances the heat transfer, thereby increasing the efficiency of the collector.

New method for the design of radiant floor cooling systems with solar radiation

Impacts of solar shortwave radiation are not taken into account in the standardized design methods in the current radiant system design guidelines. Therefore, the current methods are not applicable for cases where incident solar is significant. The goals of this study are to: (1) use dynamic simulation tools to investigate the impacts of solar radiation on floor cooling capacity, and (2) develop a new simplified method to calculate radiant floor cooling capacity when direct solar radiation is present. We used EnergyPlus to assess the impacts of solar for different design conditions. The simulation results showed that the actual cooling capacities are in average 1.44 times higher than the values calculated with the ISO 11855 method, and 1.2 times higher than the ASHRAE method. A simplified regression model is developed to improve the predictability of ISO methods. The new model calculates the increased capacity as a function of the zone transmitted solar and the characteristic temperature difference between the hydronic loop and room operative temperature.

Historical trends and current state of heating and cooling degree days in Italy

Degree days (DD) represent a versatile climatic indicator which is commonly used in the analysis of building energy performance, as e.g. (i) to perform energetic assessment of existent and new buildings, (ii) to analyze the territory energy consumption, (iii) to develop scenario analyses in terms of energy consumption forecasting, and so on.Different methods can be used for determining the DD values, depending on the available climatic data of each location. In the present paper, the simplified methods based on reduced climatic data set have been compared assuming the mean daily degree-hours method (MDDH) as reference. Hourly temperature profiles recorded by the meteorological station located at the University of Genoa have been used for these analyses.In the second part of the present work, the ASHRAE method has been selected to calculate heating (HDD) and cooling (CDD) degree days for several Italian cities. In particular, daily meteorological data of several Italian cities (covering the whole climatic conditions which occur in Italy) have been used to calculate heating and cooling degree days in the period 1978–2013, in order to analyze their trends in the last years. Finally, the historical profiles of Rome and Milan have been treated as time-series and analyzed in the frequency domain, performing a decomposition of the original data set into different characterizing components. This simplified approach permits to deeply analyze the historical profile of DD and represents a simple starting point method for future analyses with forecasting perspectives.

Flammability limits of binary mixtures of dimethyl ether with five diluent gases

Flammability limits of binary mixtures of dimethyl ether with five kinds of diluent gases were measured by ASHRAE method at room temperature. The five diluent gases are nitrogen, carbon dioxide, chlorodifluoromethane (HCFC-22), 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea). The experimental results were correlated with the extended Le Chatelier's formula. It was found that the experimental results were well reproduced by the formula. In addition, flammability limits of binary mixtures of dimethyl ether with nitrogen and carbon dioxide were compared with the estimated values based on the adiabatic flame temperature method. The experimental results were found to be in satisfactory agreement with the estimated values.

Effect of high humidity on flammability property of a few non-flammable refrigerants

The effect of high humidity on the flammability property was examined in air for non-flammable refrigerant materials of R-410A, R-410B, R-134a, and R-125. The high humidity here means the relative humidity of up to 50% at 60°C. The measurements were done in a 12L spherical glass flask following the ASHRAE method. Under the present humidity condition, R-410A, R-410B, and R-134a became flammable, whereas R-125 did not. For the first three samples, the limiting humidity condition to make the gas flammable was determined. In addition, the effect of temperature up to 100°C on the flammability property was examined for these materials at the relative humidity of 50% corrected for 23°C. All four samples remained non-flammable under this condition. For comparison, flammability limits of several flammable compounds were also measured under similar conditions.

Flammability Limits of Binary Mixtures of 1,2-Ethanediol + Steam and 1,2-Propanediol + Steam

Flammability limits of binary vapor mixtures of 1,2-ethanediol + steam and 1,2-propanediol + steam were measured by the ASHRAE method. The test temperatures were 473 K for 1,2-ethanediol + steam and 463 K for 1,2-propanediol + steam. The observed values were analyzed by the extended Le Chatelier’s formula. It was found that the experimental results were excellently reproduced by the formula. In addition, the experimental results were compared with the estimated values based on the adiabatic flame temperature method. The observed values of lower flammability limits were in good agreement with the estimated values, and those of upper flammability limits were within acceptable deviations.

Flammability limits of binary mixtures of ammonia with HFO-1234yf, HFO-1234ze, HFC-134a, and HFC-125

Flammability limits of binary mixtures of ammonia with HFO-1234yf, HFO-1234ze, HFC-134a, and HFC-125 were measured in dry air. The measurements were made in a 12L spherical glass flask using ASHRAE method. It has been found that the flammability limits of ammonia and HFO-1234yf mixtures are extremely different from the values predicted by Le Chatelier's equation. Modification of Le Chatelier's equation was made by introducing Ellipse function to analytically express the flammability limits of the mixtures of arbitrary concentrations. HFO-1234ze is non-flammable in dry air, but becomes flammable if ammonia is added more than four percent. If the content of ammonia exceeds 20 percent, the values of flammability limits become very close to the corresponding ones for HFO-1234yf and ammonia. On the other hand, the flammable regions of ammonia mixed with each of HFC-134a and HFC-125 are much narrower than the mixtures of HFO-1234ze. Extension of the ellipse modified Le Chatelier's equation introduced in the above was made to successfully explain the flammability limits of these mixtures.

Design of borehole heat exchangers for ground-source heat pumps: A literature review, methodology comparison and analysis on the penalty temperature

Better energy efficiency of ground coupled heat pump systems in comparison with traditional applications leads to continued growth in the number of installations for space conditioning. The solution with vertical heat exchangers is the most widespread. The design of the borehole heat exchangers (BHEs) is a nodal point, both from an energy efficiency and an economic point of view.In literature, several methods to design these systems are available. However, to promote their application, easy-to-use procedures are required; furthermore designers very often are discouraged from the use of not-open or complicated computational tools. Among the literature models, the ASHRAE method is surely the simplest procedure and, as a consequence, it is suitable for this goal. In this approach, sizing of the BHE length is strongly affected by the parameter named penalty temperature, which is an index to evaluate the long-term behaviour of the borehole field.In this paper, a review of this index is reported and in addition a new approach for its evaluation is presented. Furthermore, a detailed analysis of the proposed method is performed on a real case-study building with only heating conditioning.

On the temperature dependence of flammability limits of gases

Flammability limits of several combustible gases were measured at temperatures from 5 to 100°C in a 12-l spherical flask basically following ASHRAE method. The measurements were done for methane, propane, isobutane, ethylene, propylene, dimethyl ether, methyl formate, 1,1-difluoroethane, ammonia, and carbon monoxide. As the temperature rises, the lower flammability limits are gradually shifted down and the upper limits are shifted up. Both the limits shift almost linearly to temperature within the range examined. The linear temperature dependence of the lower flammability limits is explained well using a limiting flame temperature concept at the lower concentration limit (LFL) – ‘White's rule’. The geometric mean of the flammability limits has been found to be relatively constant for many compounds over the temperature range studied (5–100°C). Based on this fact, the temperature dependence of the upper flammability limit (UFL) can be predicted reasonably using the temperature coefficient calculated for the LFL. However, some compounds such as ethylene and dimethyl ether, in particular, have a more complex temperature dependence.

Thermal performance testing of flat-plate collectors

Existing standards for testing the performance of flat-plate solar collectors are documented in ASHRAE 93 [ANSI/ASHRAE Standard 93-2003, 2003. Methods of Testing to Determine Thermal Performance of Solar Collectors, ISSN: 1041-2336, ASHRAE, Inc., 1791 Tullie Circle, Ne, Atlanta, GA30329], ISO 9806-1 [ISO Standard 9806-1:1994(E), 1994. Test Methods for Solar Collectors – Part 1: Thermal Performance of Glazed Liquid Heating Collectors Including Pressure Drop, ISO, Case Postale 56, CH-1211 Geneve 20, Switzerland] and EN12975-2 [European Standard EN12975-2:2001, 2001. Thermal Solar Systems and Components – Solar Collectors – Part 2: Test Methods, CEN, Rue de Stasart, 36, B-1050, Brussels]. The ASHRAE 93 standard requires an experimental determination of the steady-state collector efficiency under prescribed environmental conditions for a range of collector fluid temperatures. Each test requires a minimum of 20 min and 22 tests are required to fully characterize a collector’s thermal performance. The ASHRAE 93 testing procedure is further complicated by the fact that the prescribed weather conditions do not often occur in some locations, which prolongs the time required to conduct the performance tests for a given collector. The EN12975-2 collector test procedure provides an alternative transient test method that can be conducted over a larger range of environmental conditions. This paper compares the results obtained by applying the EN12975-2 standard with results obtained from the ASHRAE 93 steady-state tests for a well-designed single-glazed selective surface flat-plate collector. The collector thermal parameters, F R ( τα) e and F R U L obtained by the two test methods show good agreement. The incident angle modifier coefficient determined in the ASHRAE method, which uses a separate test for this purpose, was found to be more accurate than that determined in the transient method according to the EN12975-2 standard, which obtains this value and all other collector parameters in the same step. This transient method, however, uses a refined collector model that includes specific terms for the wind speed dependence and the collector thermal capacitance, which are absent in the ASHRAE model. The long-term collector thermal performance as a part of a water heating system was simulated using the efficiency curves derived from each of the test methods. The solar fractions obtained by simulation are within 7% for both cases.

Flammability limits of isobutane and its mixtures with various gases

Flammability limits of isobutane and five kinds of binary mixtures of isobutane were measured by the ASHRAE method. Propane, nitrogen, carbon dioxide, chloroform, and HFC-125 (1,1,1,2,2-pentafluoroethane) were used as the counter part gases in the mixtures. The observed data were analyzed using the equations based on Le Chatelier's formula. The flammability limits of mixtures with propane were well explained by the original Le Chatelier's formula. The flammability limits of mixtures with nitrogen and the ones with carbon dioxide were adequately analyzed by the extended Le Chatelier's formula. It was found that the extended Le Chatelier's formula is also applicable to the flammability limits of mixtures with chloroform and HFC-125.

Measurement and numerical analysis of flammability limits of halogenated hydrocarbons

Flammability limits measurement was made for a number of halogenated compounds by the ASHRAE method. Most of compounds measured are the ones for which discrepancy was noted between the literature values and predicted values of flammability limits. As a result, it has been found that most of the newly obtained values of flammability limits are not in accordance with the literature values. Numerical analysis was carried out for a set of flammability limits data including the newly obtained ones using a modified analytical method based on F-number scheme. In this method, fitting procedure was done directly to flammability limits themselves instead of fitting to F-number. After the fitting process, the average relative deviation between the observed and calculated values is 9.3% for the lower limits and 14.6% for the upper limits.

Climate effect on the evaluation of the heat transfer through the perimetral structures of refrigerating stores

Numerical simulation gives the possibility to evaluate, with the approximation peculiar to the method, the temperature trend and the heat exchange through the outside perimetral structures of the refrigerating stores, under different climatic conditions. Specifically, two types of structural panels used in the refrigerating stores building are analysed. Taking in account the climatic sectors under which our national country could be divided, the authors evaluated the sun and the outside temperature influence on the structures thermal behaviour. Using numerical simulation, the thermal power exchange and the temperature field had been determined, under different climatic situations and for a seasonal mean day, related to the exposition and the thermophysical characteristics of the materials. The obtained results show the difference of the thermal behaviour of the two different structures considered and have been utilized for a comparison with the ASHRAE method.