Backup Heating Research Articles

A simulation study on a water chiller complete with a desuperheater and a reversibly used water cooling tower (RUWCT) for service hot water generation

In sub-tropical regions, a standard water cooling tower may be reversibly used, as part of a desuperheater heat recovery system for service hot water heating, to extract free heat from ambient air in colder seasons when building cooling load is reduced. Part of chilled water is pumped into a RUWCT where it is heated by warmer ambient moist air. This paper presents a simulation study where a steady-state mathematical model for such a desuperheater heat recovery system complete with a RUWCT has been developed. Simulation results based on the specifications of an actual chiller plant have demonstrated that the model developed is stable and behaves as expected. With the model developed, the operating characteristics of the refrigeration system with a desuperheater and a RUWCT were studied. The required flow rate of chilled water to be pumped into the RUWCT was calculated in order to satisfy a certain heat load. The maximum heating capacity of the system under different operating conditions were also evaluated. The simulation results also indicated that the use of a RUWCT would achieve a higher energy efficiency than the use of electrical heating as backup heat provisions when building space cooling load is reduced.

Natural convection solar dryer with biomass back-up heater

A direct-type natural convection solar dryer and a simple biomass burner have been combined to demonstrate a drying technology suitable for small-scale processors of dried fruits and vegetables in non-electrified areas of developing countries. From a series of evaluation trials of the system, the capacity of the dryer was found to be 20–22 kg of fresh pineapple arranged in a single layer of 0.01-m-thick slices. The overall drying efficiency of the unit was calculated to be ∼9%. During the same trial, the drying efficiency of the solar component alone was found to be 22%. Other trials estimated the efficiency of the burner in producing useful heat for drying to be 27%. Key features of the biomass burner were found to be the addition of thermal mass on the upper surface, an internal baffle plate to lengthen the exhaust gas exit path and a variable air inlet valve. Further modifications to further improve the performance of both the solar and biomass components of the dryer are suggested.

Modeling an Integral Dual Solar/Gas-Fired Generator for a Water-Lithium Bromide Absorption Chiller

This paper presents a design procedure for a dual solar/gas-fired generator of an absorption chiller. The solar energy is the primary driving source for the generator, while the natural gas serves as the backup heat when the solar energy is unavailable or insufficient. Saturated forced convective boiling for binary mixtures has been considered to account for the reduction in the heat transfer coefficient observed for most mixtures. The simultaneous solar and gas-fired desorption process was investigated. The generator constructed based on modeling results yielded good performance in the experiment. [S0195-0738(00)00704-4]

Technical note Best connection scheme of collector modules of thermosyphon solar water heater operated at high temperatures

Large scale thermosyphon solar water heater for high temperature applications is simulated by the use of the Transient Simulation Program (TRNSYS). A daily hot water load of 1500 l/day and 2500 l/day at 80°C was assumed. The hot water is consumed daily from 08·00–17·00 h. A back-up electric auxiliary heater was added to the system in two schemes: first, located inside the storage tank with a thermostat; second, outside the tank connected to the heating system between the tank and the facilities. The collector modules were connected in five different schemes: first, all collectors were connected in series in one line, or collectors were connected in two, three, four or five parallel lines each consisting of many collectors. The results showed that the best connection is when the 20 collectors, comprising the system, are connected in two parallel lines each consisting of 10 collectors. It was found that the monthly and yearly useful energy from the system was higher when the auxiliary water heater was added to the system outside the storage tank.

Air-cooled heat pump with desuperheater: Retrofit for year-round service hot water supply

In a case study project an air-cooled heat pump unit was retrofitted with a desuperheater to provide service hot water in addition to chilled water for comfort space cooling in a 24-room holiday villa located in a subtropical region. The retrofit project is described, and system operating performance and energy efficiency are reported. A standard cooling tower was used to extract free heat from ambient air in transitional seasons, thus eliminating the need for electric back-up heating for service hot water.

Back-up heater

Back-up heater

太陽熱利用給湯システムにおける貯湯槽内の温度性状と補助熱源機の稼働制御に関する研究

The authors manufactured a hot water supply system with solar panels. Water in a storage tank was heated by the fluid path through solar panels and a heat-pump as a back-up heater. This system was operated in three modes through a year, and following results were obtained. (1) In the case that using pattern of the hot water was based on an energy conservation handbook, the maximum hot water demand occurred in supplying to a bathtub. Then for the maximum demand it was necessary to prepare 300l hot water which was more than 50℃, in the storage tank. In other time, it was necessary to prepare 100l hot water which was more than 50℃. (2) The efficiency of solar energy to heat water in the storage tank was obtained. The prediction control of heat-pump operation was possible by using neural network. Furthermore, the authors showed an operation control method to supply for the maximum demand of hot water and to conserve energy.

The magic of solar adobe

This article describes the energy efficient features of a house in Santa Fe. It is a modern version of ancient adobe house of the area. The homes solar features added no net cost to its construction and save more than 80% on conventional energy use. Topic areas covered are as follows: art of adobe; solar design; back-up heat; energy and cost performance.

95/03750 Direct solar floor heating with incorporated back-up heat supply

95/03750 Direct solar floor heating with incorporated back-up heat supply

Single-tube integrated collector storage systems with transparent insulation and involute reflector

Integrated collector storage (ICS) systems, consisting of a pressure-resistant single tube absorber in front of an involute reflector and covered by highly transparent insulation material, have been developed. Compared to the earlier multiple-tube design the system performance has been improved. For an absorber area of 4.2 m 2 in Freiburg (W. Germany) and a hot water demand of 160 liters/day, the annual solar fraction of the system is 65% with an annual efficiency of 32% (required hot water temperature is 45°C). There is no risk of freezing. Detailed computer simulations for the ICS and the back-up heating system have been made and show the influence of various parameters on the system performance. Compared to conventional solar domestic hot water systems the performance of the ICS systems is almost as good as that of systems with vacuum tube collectors but ICS systems require much less complicated technology.

Plate recuperators used with air/air heat pumps in building ventilation systems

The economic viability of stand-alone heat pumps for space heating is limited by the achievable coefficient of performance. By combining the heat pump with a plate recuperator in full fresh air systems the average heating season efficiency can be increased to the equivalent of a COP of 6. The system works both as a heating and cooling system and will provide over 90% of annual energy requirement, making the use of central heating plant for back-up heating uneconomical. The resulting capital cost saving can be used to offset in part or in full the extra capital cost of the heat pump equipment.

Prediction of the hourly temperature in a Kuwaiti house

Abstract The bihourly room temperature inside a passively designed house in Kuwait, without backup heating and cooling, is studied, for both the original design and with the addition of thermal insulation to the house walls and roof. The calculations were performed using the Goldstein-Lokmanhekim method to find the floating temperature inside the house and to see the effect of thermal insulation on this temperature and also on the energy requirement when mechanical cooling is used. Results show that adding insulation will reduce the cooling energy requirement, but insulation is found to be unnecessary when no mechanical cooling is used.

Thermal performance tests of a solar thermosyphon domestic hot water system in Dhahran, Saudi Arabia

Abstract Thermal performance tests were made on a commercial thermosyphon solar domestic hot water system during the four seasons of the year in Dhahran (Lat. 26°18′N, Long. 50°08′E), Saudi Arabia. The system had an effective collector area of 3·76 m 2 , a 300-l storage tank and an electric auxiliary heater. The tests were run outdoors using an automatically controlled hot water drawoff valve which provided a daily water use profile thought to be representative of local use and totalling 300 l per day. The yearly average solar fraction and thermal efficiency values were 77·5 and 31% respectively. Included in the test program were single sample measurements of storage water heat recovery and collector array efficiency. The recovery rates for solar plus electric backup heater and solar only were 2·7 and 6·3 h respectively. The average collector array efficiency was 55% for the 1-day test.

Performance details of a rotating prism solar wall

The “kinetic wall” discussed in the First International Symposium in this series has been incorporated into a passive solar house that was built at Sede Boqer, Israel. The house has been lived in and monitored since October 1982. The present paper shows an analysis of the first winter's thermal performance figures of the rotating prism wall and compares it with some more conventional passive heating methods that are employed in the other rooms of the house. During the heating period from November 1st 1982 until March 31st 1983, the average ambient temperature at Sede Boqer was 10.5°C with a mean diurnal temperature swing of ±5.0° C. By contrast, the average air temperature in the room heated by the kinetic wall was 18.0°C with a mean diurnal temperature swing of magnitude less than ±1.0° C. No backup heating was necessary in this room. The rotating prism wall has proved to be easy to realize, convenient to live with and a remarkably effective space heating device.

A TRNSYS/GROCS Simulation of the TECH House I Ground-Coupled Series Solar-Assisted Heat Pump System

The series solar-assisted heat pump heating system with ground-coupled storage in The University of Tennessee’s TECH House I in Knoxville, Tennessee, has been modeled using TRNSYS/GROCS and was compared to the experimental performance for the 1980–81 heating season. The simulation results were within 8 percent of the experimental measurements. Both simulation and experimental results showed that ground coupling of thermal storage led to the elimination of electric resistance backup heat and a large reduction in the peak heating demand of the house. Results of a parametric study showed that, in general, a ground-coupled storage tank performs better than a storage tank placed outdoors in the Knoxville area. Application of a next generation heat pump resulted in the most significant impact on the seasonal performance factor. As expected, higher performance collectors and larger collector areas led to higher system seasonal performance. An economic analysis showed that the series solar heat pump system cannot economically compete with the stand-alone heat pump system in the Knoxville area.

Magnetic properties of Ga:YIG with laser irradiation in inert gas

Magnetic properties of substituted iron garnet films can be changed locally by laser irradiation (annealing and quenching ). We have investigated laser annealing with furnace back-up heating in O 2 , N 2 and Ar gas over a wide range of temperature. In air, laser annealing with high temperature back-up heating above 700°C resulted in domain width reduction with both M s and K u increased differing from other reports. In inert gas, laser annealing with rather low temperature back-up heating is expected to vary magnetic properties locally which is different from that produced by high temperature heating since produced oxygen vacancies lower the activation energy and the relaxation time for cation migration. Only with back-up heating below 650°C, we succeeded high quality annealing in inert gas. Our re-annealing experiment of this film showed that low temperature laser annealing might have lowered the saturation magnetization which is not performed in air. We have found wide temperature range of reversible laser annealing.

Back-up electrical power needs for residential solar water heaters

Abstract Increasing prices for electricity have resulted in a rapidly growing demand for residential solar water heating systems. Most of the solar systems being sold and installed include an electrical powered back-up heater for use during sustained periods of low solar insolation, or periods of excessive hot water use. This electrical back-up use has prompted some utilities to consider establishing very high rates for owners of solar systems. The purpose of this paper is to report on a study to simulate a typical solar installation and determine the probability that back-up power will be needed at the time the utility experiences its peak load. The result of this computer study for one geographic area provides a quantitative basis to show that there is little justification for charging solar water heater owners higher rates than other residential customers.

A series connected solar air heating system using the FMTC collector and the rolling cylinder heat store

An annual performance simulation has been carried out using the FMTC collector, the rolling cylinder heat store with Glauber's Salt, and a dwelling, all arranged in a series connected solar air heating system. The results suggest that a modest size system can readily carry the entire heating load of an energy efficient home in any geographical region of the U.S. The energy required to drive the system, i.e. rolling cylinder drive energy plus air blower drive energy, is always an important fraction of the total system output. In Boston 1958 weather the seasonal COP varies from 2.5 to 5.8 depending on the particular rolling cylinder design configuration selected. 90 per cent of the system drive energy is base load for the electric utility. There are no “coldest day peaks” resulting from electric backup heating. A system using the highest drive energy configuration may be sized for 99.5 per cent solar system heating using the same design chart at any northern region of the U.S.A. One system sized for Boston was evaluated at seven other geographical locations. The resulting house size was always in the acceptable range. This raises the possibility that one or a few standardized system sizes could serve an area as large as the U.S. Individualized solar system design calculations would not be necessary. Cloudy weather performance was noticeably improved in Boston (1958 weather). On a seasonal basis the FMTC collector delivered three times more heat than a typical flat plate (TFP) collector and 60 per cent of that heat was collected at insolation levels which were below the functional cut-off level of the TFP collector.

Pompes de chaleur à transferts thermiques sans auxiliaires, à convection naturelle et rayonnement

With many conventional heat pump systems the energy absorbed by auxiliary equipment (fans, defrosters, pumps) can be higher than the power used by the compressor. For example, with a particular air-air heat pump system the annual energy consumption of the compressor and its crankcase heater is 11 240 kWh, whilst 21 501 kWh of energy are consumed by auxiliary fans, the defrost unit, back-up heating and system heat losses. Some savings can be made by monitoring the interior unit fan to correspond to the running time of the compressor or by increasing the size of the heat pump in order to reduce back-up heating, but the latter solution has proved to be costly. Laboratory experiments since 1976 have been to reduce power consumption of auxiliaries, particularly air-air and air-water systems, by using a solar collector as the heat pump evaporator. The collector is made up of flat plates oriented in such a manner as to receive direct solar radiation, with both faces of the plates absorbing energy from the surrounding air by natural convection. The faces of the plates exposed to solar radiation are preferably painted black, but other colours with a low coefficient of reflection (eg brown, brick red, dark green, etc.) can be used if the evaporator-collector is to be architecturally pleasing. Glazing is not necessary, as is usually the case with solar panels. The collector-evaporator plates, and associated piping, are precharged with refrigerant and ready for connection to the heat pump circuit. A heat pump equipped with this collector-evaporator will provide an annual energy saving of 30% as compared to a standard air—water system. Additional benefits are no defrosting cycles, simplified installation, greater operational reliability, and an increased system COP. A table sets out the performance parameters of this system to show the incidence of back-up solar energy during the months of lesser solar radiation, ie outside the months of June to September, eg the COP during daylight hours (a minimum of about 7 h in December, to a minimum of 14 h in May) averages out at 3.89, and 3.27 during nocturnal hours. The article also describes a water heating system (200 and 300 I) using this collector-evaporator, an air-air heat pump with static (no forced ventilation) heat exchangers, and an air-water system using a static evaporator which will provide a 25% energy saving over its conventional counterpart.

The performance of a well insulated house heated by an air-water heat pump

SYNOPSIS This paper describes the performance of a highly insulated house operated under simulated occupancy and heated by an air-water heat pump during 1978–80. The house, which was one of four BRE low energy house laboratories, was heated continuously to 20°C. Although underfloor heating coils were employed. (in order to provide a low condensing temperature for the heat pump) the control of internal temperatures was largely satisfactory being within ± 2°C of the mean value on over 85% of occasions. The seasonal coefficient of performance of the heat pump for space and hot water heating was 2.3 which in primary energy terms corresponds to a natural gas boiler of about 70% efficiency. The heat demand of the dwelling at −1°C was 3.8 kW which was close to the expected value and the heat pump required backup heating only during some defrosts. The backup heating system was used in the true supplementary mode only on 2 days during the winter of 1978/79.