This paper describes technology for an environmentally friendly split type air conditioner, characterized by using safe amounts of propane as refrigerant. The objective was to demonstrate a system, using less than 150 g of propane, providing minimum 3.5 kW cooling capacity with a COP2 >= 3.5 at air flows that allow acceptable noise levels. The condenser and evaporator were of standard microchannel type. The evaporator headers were rebuilt to reduce charge and different techniques were tested for even refrigerant distribution. A DC-motor scroll compressor for AC in electric vehicles was used, characterized by small internal volumes, small oil charge and wide capacity range (800-8500 rpm). The system also included a specially built minichannel liquid/suction line heat exchanger and a standard electronic expansion valve. The connection lines in-between the indoor and outdoor unit were 6 m long. The project target was reached with a charge of 143 g propane.

The EcoPac project comprises of the development and evaluation of a heat pump with low charge of R600a (isobutane), optimized for a low temperature lift. The cold side operates at temperatures of 15 to 35 degrees C and the high side temperatures are 50 to 70 degrees C. This paper describes the heat pump when used as a standalone unit with water as heat transfer fluid. The following results have been attained with a charge of 120g of R600a: . output of heat in the range of 2 up to 12 kW, . a maximum output of heat of 1kW per 10 g of refrigerant and . Coefficient of performance of 3,3 up to 11 depending on operating condition.

In a conventional heat pump system, the throttling of the warm refrigerant liquid in the expansion valve is one of the main losses. One way to reduce these losses is to sub-cool the fluid before it enters the expansion valve. This project will investigate the possible benefits of using an "economizer", sometimes called a mechanical subcooler. By means of this the heating capacity can be increased as well as the COP of the system. The intention of the project is to use an economizer unit in the form of a small high temperature heat pump with isobutane, R600a, as refrigerant. This unit, in short here called an Ecopac-unit will thus be used as an economizer for a larger propane, R290, heat pump, but could potentially also be used for other refrigerants in the main system. The hot side of the isobutane heat pump can be used for heating of hot tap water i.e., temperatures in the range of 50-70 degrees C. The isobutane heat pump will use the liquid refrigerant after the condenser as heat source and will hence sub-cool the refrigerant fluid in the main heat pump. The isobutane heat pump will be working with evaporating temperatures in the range of 15-35 degrees C. In this paper the potential performance of such a system is simulated and some initial experimental results are given.

This paper describes the technology for an environmentally friendly ground source heat pump for a single family home, characterized by using pure water as coolant and propane as refrigerant. The objective was to build a test system, operating under realistic conditions, using less than 150 g of propane, providing at least 5 kW heating capacity with reasonable efficiency and without freezing the coolant water. The borehole heat exchanger was of coaxial type, providing about half the thermal resistance compared to a standard U-tube collector (Acura 2010). The evaporator and condenser where asymmetrical plate heat exchangers with small channel height (< 1 mm) on the refrigerant side. They were developed and manufactured exclusively for this project with a new type of press pattern, including a special, small volume sub-cooling section at the end of the condenser. A DC-motor scroll compressor for AC in electric vehicles was used, characterized by small internal volumes, small oil charge and wide capacity range (800-9000 rpm). A PAG-type oil was used, which however seemed to cause some problems with heat transfer and pressure drop in the evaporator. The system also included a specially built mini channel liquid/suction line heat exchanger and a standard thermostatic expansion valve. The paper presents test results for a heating capacity range of 2-10 kW. The performance was reasonable in this range with a charge of 100 g of propane (-1<T-2<5 degrees C, 30<T-1<55 degrees C). The charge that is required is determined at the lowest capacities, at low compressor speed and high evaporating pressures. A lower charge is beneficial at higher capacities.

Indirect systems with secondary (working) fluid circuits are often used where there are many places to be cooled or where long pipes are required. Examples of systems with many places to be cooled ...

I den har boken far du lara dig mer om bergvarmepumpar. Hur fungerar en varmepump? Hur gor man en lonsamhetskalkyl? Hur upphandlar man? Kan man trimma sitt system? Dessutom: lar dig mer om radiator ...

A prototype liquid-to-refrigerant heat exchanger was developed with the aim of minimizing the refrigerant charge in small systems. To allow correct calculation of the refrigerant side heat transfer, the heat exchanger was first tested for liquid-to-liquid (water-to-water) operation in order to determine the single-phase heat transfer performance. These single-phase tests are reported in this paper. The heat exchanger was made from extruded multiport aluminium tubes and was designed similar to a shell-and-tube heat exchanger. The heat transfer areas of the shell-side and tube-side were approximately 0.82 m2 and 0.78 m2, respectively. There were six rectangular-shaped parallel channels in a tube. The hydraulic diameter of the tube-side was 1.42 mm and of the shell-side 3.62 mm. Tests were conducted with varying water flow rates, temperature levels and heat fluxes on both the tube and shell sides at Reynolds numbers of approximately 170–6000 on the tube-side and 1000–5000 on the shell-side, respectively. The Wilson plot method was employed to investigate the heat transfer on both the shell and tube sides. In the Reynolds number range of 2300–6000, it was found that the Nusselt numbers agreed with those predicted by the Gnielinski correlation within ±5% accuracy. In the Reynolds number range of 170–1200 the Nusselt numbers gradually increased from 2.1 to 3.7. None of the previously reported correlations for laminar flow predicted the Nusselt numbers well in this range. The shell-side Nusselt numbers were found to be considerably higher than those predicted by correlations from the literature.

This paper presents heat transfer data for a multiport minichannel heat exchanger vertically mounted as an evaporator in a test-rig simulating a small water-to-water heat pump. The multiport minichannel heat exchanger was designed similar to a shell-and-tube type heat exchanger, with a six-channel tube of 1.42 mm hydraulic diameter, a tube-side heat transfer area of 0.777 m(2) and a shell-side heat transfer area of 0.815 m(2). Refrigerant propane with a desired vapour quality flowed upward through the tubes and exited with a desired superheat of 1-4 K. A temperature-controlled glycol solution that flowed downward on the shell-side supplied the heat for the evaporation of the propane. The heat transfer rate between the glycol solution and propane was controlled by varying the evaporation temperature and propane mass flow rate while the glycol flow rate was fixed (18.50 l min(-1)). Tests were conducted for a range of evaporation temperatures from -15 to +10 degrees C, heat flux from 2000 to 9000 W m(-2) and mass flux from 13 to 66 kg m(-2) s(-1). The heat transfer coefficients were compared with 14 correlations found in the literature. The experimental heat transfer coefficients were higher than those predicted by many of the correlations. A correlation which was previously developed for a very large and long tube (21 mm diameter and 10 m long) was in good agreement with the experimental data (97% of the data within 30%). Several other correlations were able to predict the data within a reasonable deviation (within 30%) after some adjustments to the correlations. (C) 2008 Elsevier Ltd and IIR. All rights reserved.

This paper reports heat transfer results obtained during condensation of refrigerant propane inside a minichannel aluminium heat exchanger vertically mounted in an experimental setup simulating a water-to-water heat pump. The condenser was constructed of multiport minichannel aluminium tubes assembled as a shell-and-tube heat exchanger. Propane vapour entered the condenser tubes via the top end and exited sub-cooled from the bottom. Coolant water flowed upward on the shell-side. The heat transfer areas of the tube-side and the shell-side of the condenser were 0.941m2 and 0.985m2, respectively. The heat transfer rate between the two fluids was controlled by varying the evaporation temperature while the condensation temperature was fixed. The applied heat transfer rate was within 3900–9500W for all tests. Experiments were performed at constant condensing temperatures of 30°C, 40°C and 50°C, respectively. The cooling water flow rate was maintained at 11.90lmin−1 for all tests. De-superheating length, two-phase length, sub-cooling length, local heat transfer coefficients and average heat transfer coefficients of the condenser were calculated. The experimental heat transfer coefficients were compared with predictions from correlations found in the literature. The experimental heat transfer coefficients in the different regions were higher than those predicted by the available correlations.

Enormous quantities of heat are available in air, soil, water, exhaust air from buildings, and in waste water of any kind. However these heat sources are use-less for heating purposes since their temperatures are lower than the tempera-ture required for heating. Heat pumps can be used to extract heat from these sources with a small expenditure of additional energy and up-grade and deliver the energy as useful heat for room heating. The heat pump cycle employs the well-known vapour compression cycle. The amount of heat delivered by a heat pump is equal to the amount of energy extracted from the heat source plus the heat equivalent to the compression work of the heat pump. Heat pumps, of course, are being generally accepted as outstanding energy saving units due their coefficient of performance (COP). Heat pumps for house heating have been used extensively in many countries and are especially common in Sweden. The annual growth rate of heat pump usage in Sweden is the same as in rest of Europe. According to the Swedish heat pump association, between 1986 to August 2003, the number of installed heat pump units in Sweden was 332,309. The demand for heat pumps started to increase from the year 1995 and in the year 2002, approximately 40,000 heat pump units were installed. Among the many types available, single-family heat pumps providing heating capacity of about 5 kW are widely popular. The main drawbacks of heat pumps are the complexity of the systems, high cost, need of technical knowledge, safety hazards and environmental effects of certain refrigerants, etc. An efficient heat pump with small refrigerant charge would have less of some of these drawbacks and could be a competitive alterna-tive to other heating processes. In this study, methods of refrigerant charge minimisation without reducing the performance of a small capacity (5 kW) heat pump have been investigated. Work has been focused on finding refrigerant charge distribution in different components of the heat pump, on finding out the solubility of refrigerant (pro-pane) with different compressor lubrications oils, on testing different types of compact heat exchangers, on constructing new minichannel heat exchangers and on finding correlations for calculating the heat transfer of minichannel heat exchangers. The results included in this thesis have been presented in four con-ference papers and five journal papers of which two were published and three were submitted for publication.

Modelling the Amount of Refrigerant and the Pressure Drop in a Rectangular Copper Evaporator

Div. of Applied Thermodynamics and Refrigeration, Royal Institute of Technology, KTH, Stockholm, Sweden. The energy consumption to operate auxiliaries such as fans and pumps in heat exchangers have a significant influence on the total energy demand for operating a refrigerating system. With a starting point in a simple entropy analysis a more practical approach is adopted for common cases of air coil fans in evaporators or condensers. Examples are given to illustrate how the power for evaporator or condenser fans will affect the capacity and total energy demand of refrigerating systems. It is shown that the two different criteria: -maximum of capacity or -minimum of energy demand (equivalent to maximum system COP) will give different optima for the power to be used in fans or pumps. Simple relations are derived for optimum power in fans or pumps for the two different criteria applicable for many general cases in refrigerating systems. Introduction The energy needed to operate fans or pumps is important when considering the total energy demand to operate a refrigerating plant or a heat pump. It is not unusual that the electric power of such auxiliaries is in the order of25% or more of the power to operate the compressor in a system. The purpose of this paper is to illustrate and exemplify this issue. Simple relations will be derived for optimum power in fans or pumps to reach criteria like maximum capacity or maximum system COP. Let us exemplify with the application of an evaporator. As a starting point let us assume that we have a given plant where we can adjust the fan speed in practice perhaps by means of an inverter control. It is obvious that by using a high fan speed the evaporator will operate with smaller temperature differences between the inlet air and the refrigerant evaporating temperature than if low speed is used. This will decrease the temperature lift of the cycle and thus decrease the compressor work. However we will have to pay for the fan power and what is of interest is the sum of the power for the compressor and the fan. It is obvious that there must exist a certain fan power that we can call optimal from the point of view of energy consumption. Two different approaches will be used: First a treatment minimizing the entropy generation and, secondly, a more practically oriented way of treatment will be demonstrated. This treatment will concentrate on refrigerating applications. Slightly different relations will be obtained for heat pump operation. Space limitations prevents a treatment for that case but the practical result for minimum energy demand are quite similar. Relations between pumping power and temperature difference The pumping power will influence the temperature difference for a case with given geometry. A reasonable assumption is that the overall heat transfer coefficient is proportional to Vu where Vis the fluid flow and nu is an exponent, which in most cases has a value in the range of 0,3 to 0,6. The pressure drop can be set proportional to VP where for turbulent flow np = 1,8. The pumping power, Ep, will hence (assuming constant pump efficiency) be proportional to V(np+lJ. Based on a reasoning indicated we can write the overall temperature difference, 8, as where 8=:: C·(EPFnE: nE:: _!!!!____ which hence for most cases will be in the order ofO,l to 0,2 np+] C is a constant.

The classic, conventional analysis for the thermal performance of heat exchangers is based on three assumptions: constant fluid flow rate, constant specific heat fluids, and constant overall heat transfer coefficient. Our analysis describes a general approach for analyzing the thermal performance of heat exchangers in which the overall heat transfer coefficient varies as a function of enthalpy, with the other two basic assumptions of constant mass flow rates and constant specific heats unchanged. Many heat exchangers have an overall heat transfer coefficient that is not constant. The conventional heat exchanger thermal performance analysis is correct as long as a true, area-weighted mean value is used. In many applications, however, fluids undergo a change in phase, and the heat transfer coefficient is a function of the local quality or enthalpy; hence, the true, area-weighted, mean heat transfer coefficient will be a function of the heat flux distribution. Examples are presented that illustrate the variation in overall heat transfer coefficient for an evaporation process. We present a general method for computing a true, area-weighted mean overall heat transfer coefficient that permits use of a local overall heat transfer coefficient that is an arbitrary function of enthalpy. This method allows a simple yetmore » accurate analysis of the effects of a variable overall heat transfer coefficient to be made without the use of a large mainframe computer. We then investigate (1) linear variation of local overall heat transfer coefficient with respect to enthalpy and (2) two heat transfer correlations applicable to flow-boiling inside a tube. 9 refs., 5 figs., 4 tabs.« less