E nergy Procedia 48 ( 2014 )499 – 504
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1876-6102 © 2014 The Authors. Published by Elvier Ltd.
Selection and peer review by the scienti fi c conference committee of SHC 2013 under responsibility of PSE AG
doi: 10.pro.2014.02.059
500C arn J. Banister et al. / E nergy Procedia 48 ( 2014 )499 – 504
1.Introduction
Solar-assisted heat pump (SAHP) systems bring together the strengths of solar thermal collectors and heat pumps, allowing each piece of equipment to benefit from the prence of the other. SAHP systems were investigated starting in the 1970s and have received renewed interest since the 1990s due to technological advancements [1-9]. The SAHP system investigated in this work consists primarily of a 2.494 m2 solar thermal collector (STC), a 44 kW plate-type heat exchanger (HX), a 3.8 kW heat pump (HP), and a 302.8 L domestic hot water (DHW) tank. The equipment is connected via 2-way motorized diverter valves, which provide two independent paths to charge the DHW tank via solar energy: HX and HP.
The objective of the current work is to validate a TRNSYS (TRaNsient SYstem Simulations tool) model of the described SAHP system for reprentative days from typical meteorological year (TMY) data for Ottawa, Ontario, Canada. The TRNSYS model is validated using a test rig that has been built specifically for this purpo. This work has been preceded by a paper which outlines in detail the construction, operation, and preliminary testing of said test rig [6]. The test rig allows the perform
ance of veral SAHP system configurations to be evaluated experimentally. Results are compared to output from TRNSYS simulations to validate the system model for advanced exploratory u, supporting the development of system configurations, equipment lection, and control strategies.
A full day test compris of running the experimental system over the cour of a day with the input of weather data and a water draw profile. An automatic control strategy is programmed into the apparatus to control the mode of operation lected. This system is mirrored in a TRNSYS simulation, which is the subject of the validation.
2.Method
Building upon previous work, where SAHP system modes of operation were validated using the test rig [10], TMY data is ud both to simulate system performance and validate results experimentally for a reprentative day. Weather and water draw data from the TRNSYS simulation are supplied to the test rig, allowing for direct comparison between model and experiment. The water draw profile ud is from the Canadian Standards Association Packaged solar domestic hot water systems (liquid-to-liquid heat transfer) and is listed in Table 1 [11].
The weather data included with TRNSYS was ud for the simulations and was duplicated for the ex
perimental apparatus. The experimental apparatus operates almost identically to a real SAHP system, except that the STC is substituted for an in-line electrical heater. A schematic of the model is included below in Fig. 1.
The majority of components ud in the model are standard, with the types listed below in Table 2. All the standard components are well documented within TRNSYS and are open source [12].
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The final component, HP, is a custom type programmed by the ur, making the type number arbitrary. This component completes various practical checks, such as ensuring the inlet flow conditions are within the bounds deemed acceptable. For example, it is not permitted to have the inlet temperature below 0 (°C)since freeze-up would occur in water. The energy transfer rates are calculated using the correlations established in previous work for the heat pump being ud [10]. Refer to the preceding publication for the details.
The validation process compris of running both the experimental apparatus and TRSNSY model for a particular day, recording the relevant measurements such as temperature and energy transfer, and comparing the results. Since temperature is a good indication of how much energy transfer has taken place, this is the main method of comparison ud. The volume and substance within the syst
em are constant, meaning that changes in temperature are directly proportional to the amount of energy exchanged. In addition, temperature is the primary concern when delivering domestic hot water.
C arn J. Banister et al. / E nergy Procedia 48 ( 2014 )499 – 504 501
Table 1. Daily water draw profile, from [11]
Time of day Withdrawal at
10 L/min (L)
00:00-07:00 0
07:00-08:00 5
08:00-09:00 25
09:00-10:00 0
10:00-11:00 45
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11:00-12:00 0
属火的字有哪些12:00-13:00 5
13:00-14:00 0
14:00-15:00 0
乒乓小将15:00-16:00 0
16:00-17:00 0
17:00-18:00 5
18:00-19:00 15
关于中国的古诗>巨蟹男和处女女19:00-20:00 30
花鸭20:00-21:00 20
21:00-24:00 0
Total 150
Table 2. Standard TRNSYS component names and types [12]
Component Name TRNSYS Type
Solar (Solar thermal panel) 1b
Pipe 31
Tee 11h
Div (Flow diverter) 11f
Tank (Thermal storage) 4b
Pump (Hydronic) 110
HX (Heat exchanger) 5b
Temper (Tempering valve) 11b
TMY2 (Weather) 109
CSA-A (Water draw) 14b
502C arn J. Banister et al. / E nergy Procedia 48 ( 2014 )499 – 504
Fig. 1. TRNSYS model schematic
3.Results
Two reprentative days, August 14 and October 29, were ud from the TMY to validate the model developed. The former day is typical summer weather, whereas the latter is typical fall weather.
3.1.Day 1 – August 14
This particular day is one with clear skies and very high amounts of solar irradiation. The horizontal irradiation peaks around 3600 (kJ/h·m2), providing a high amount of solar energy into the system. The resulting DHW tank average temperatures for both the experiment and simulation are including in Fig. 2. The solar irradiation throughout the cour of the day is also included for reference.
The DHW tank temperature starts around room temperature at 20 (°C) and is heated to just over 45 (°C) by the end of the day. Although the DHW tank will typically not experience temperatures as low as 20 (°C), the initial conditions were lected to ensure that the system ran for as much time as possible. In addition, it was also important to validate the model at lower than typical temperatures.
3.2.Day 2 – October 29
The cond test day, October 29, reprents a fall day where the solar irradiation is not as high as th
e summer day and experiences more variation due to cloud cover. Corresponding results are included in Fig. 3 below.
C arn J. Banister et al. / E nergy Procedia 48 ( 2014 )499 – 504 503
Fig. 2. Results comparison for TMY weather data for August 14 in Ottawa, Ontario, Canada
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Fig. 3. Results comparison for TMY weather data for October 29 in Ottawa, Ontario, Canada
