1、AN-04-8-2 (RP-1217) Operational Performance of Ground-Coupled (Closed Loop) Ground-Source Heat Pump System Pumping Alternatives Steven E. Lambert, P.E. Stephen P. Kavanaugh, Ph.D. Member ASHRAE ABSTRACT This paper provides a brief study of various ground- source heat pump (GSHP) pumping alternatives
2、. The jrst alternative is subcentral circulator pumping with various size pumping loops followed by constant-volume central pumping and then variable-volume central pumping. This study found that variable-volume central pumping provided higher avail- able diferentialpumping heads at lower energy dem
3、ands for the same flow rates than the constant-volume centralpumping and the circulatorpumping alternatives for allflow rates tested with the exception offlow rates below 22 gpm. Below 22 gpm, the circulator pumping method proved to be the pumping method of choice. This paper also proves that consta
4、nt-volume pumping is the worst energy consumer at almost every flow demand. INTRODUCTION Ground-source heat pump systems (GSHPs) can be expensive to install if the pumping system is oversized and consequently fail to realize the estimated energy savings. Vari- ous pumping methods have been tested to
5、 determine the most effective pumping system and they are discussed in this paper. A piping system was designed and built in the HVAC laboratory of the University of Alabama to simulate a typical water-source heat pump system and implemented the use of three pumping methods: (1) subcentral circulato
6、r pumping, (2) constant-volume central pumping, and (3) variable- volume central pumping. Figure 1 is a diagram of the three pumping methods simulated in the laboratories. The subcen- tral circulator pumping method contains a circulator pump at each heat pump and the central pumping methods contain
7、one central pump. The system tested in the laboratory contained 1 O water coils, a flat plate heat exchanger to simulate losses through a vertical well bore field, and associated valves, test ports, and piping. The system constructed in the laboratory is partially shown in Figure 2. Shown is the fla
8、t plate heat exchanger and immediate piping. The turbine meter is shown at the lower right corner. The heat exchanger has been piped with appro- priate valves and strainers. Also shown are water coils WC-1 through WC-4, which constitute Loop-1 of the pumping system. Loop-2 consists of water coils WC
9、-5 through WC-8. The last two coils of the system are located in the water-to-air heat pump, WAHP-1, and the water-to-water heat pump, WWHP-1, which were both included due to immediate avail- ability and location. The piping system was constructed with high-density polyethylene pipe (HDPE). This pip
10、e can be fused together by the methods of butt and socket fusion. Once the system was built, it was filled with water and pressurized with city make- up water to 15 psig. Minor leaks were detected and repaired. Once the system was leakproof, the system was flushed to remove particulates of pipe, tap
11、e, dirt, and trapped air. The series of tests began after the system was purged of air and particulates and was leakfree. Circulator pumps P-1 through P-8 were located at water coils WC-1 through WC-8. Pump P-9 was located with the water-to-water heat pump (WWHP-1) while P-10 was located with the wa
12、ter-to-air heat pump (WAHP-1). Circulators were sized based on 2.5 gpdton of coil capacity. This smaller flow rate resulted in lower head loss for the system. The system head loss was calculated to be 42 feet of head loss, while the lower circuit setter flow rates resulted in a design head loss of 2
13、9 feet. Each coil and heat pump contained a circuit setter, Steven Lambert is a graduate student and Steve Kavanaugh is a professor in the Department of Mechanical Engineering at the University of Alabama, Tuscaloosa. 02004 ASHRAE. 543 I Il- I I wc-1 wc-2 wc-3 wc-4 Loop-2 Loop-1 - IlnE *5H)1E RLQLRC
14、H - n- P-11 UOPI PHE-1 Figure I Laboratory piping schematic for central and circulator pumping. Unbalanced 100% Demand (5 springl5 wing checkvalves) 12 10 Figure 2 Piping loop I-PHE and four coils. which could be adjusted for various flow rates by measuring the pressure drop and adjusting the valve
15、as needed. A flow graph for each circuit setter was supplied by the manufacturer and relates differential pressure between the high-pressure and low-pressure ports. The differential pressure gauge was cali- brated using a column of water 100 inches in height. See Figure 3.15 in Kavanaugh et al. (200
16、3) for a detailed view of the water coil test apparatus. CIRCULATOR TESTING The first series of tests began with all circulators operat- ing. All valves were placed in the full open position and the system was allowed to operate in an unbalanced flow state. Pressure drops were measured at the circui
17、t setters located at each coil and heat pump and correlated to circuit flow. Figure 3 shows the resulting flow through each coil and the total Figure 3 Circuit $ow rates with two diferent check valve types. system flow as measured by the turbine meter. Initially, five coils were fitted with spring c
18、heck valves and the other five were fitted with swing check valves. Notice that ail coils containing spring check valves experienced lower flow rates. The total system power is shown and was measured with a handheld power meter. Measurements were calibrated and periodically verified with a three-pha
19、se power analyzer. All circulators were electrically wired to the same disconnect, which facilitated the ease of measuring total system power. A power transducer was electrically wired in series with the single-phase service provided to the ten circulators. The transducer is configured such that a 1
20、0 volt output to the digi- tal multimeter corresponds to a 3 kW power consumption through the transducer and consequently by the circulator pumps. The voltage output to the multimeter has a linear rela- tionship with the power consumption of the system such that 544 ASH RAE Transactions: Symposia Ba
21、lanced Flow Rates at Various Demands (100%. 70%. 30%. 10%) P-2 P-5 Figure 4 Individual circulatorflo. loads-ten-pump system. P-8 rates at various , atem a 1 volt reading on the multimeter would correspond to 0.3 kW of power consumption. The accuracy of the handheld power meter was given as -t2% of r
22、eading plus one digit. Individual circulator performance curves were tested and are shown in Kavanaugh et al. (2003). The second test was performed on the ten circulators in the unbalanced position, but replacing the five spring check valves with five swing check valves identical to those already in
23、stalled. While the total system flow rate only increased 2 gpm, the individual circulators were more evenly balanced, indicating that spring check valves of the same size will increase head losses through their respective piping network. Total system power dropped from 1569 watts consumed in the unb
24、alanced system containing five spring and five swing check valves (see Figure 3) to 1557 watts in the unbalanced system containing ten swing check valves. With total system flow increasing, the power consumption would be expected to increase, but in this instance the power consumption decreased due
25、to changing only one aspect of the piping system. A test was performed on the circulators with unbalanced flow demands of 70%, 30%, and 10% of full load. This was accomplished by closing valves on three circulators to achieve 70% demand, seven circulators to achieve 30% demand, and nine circulators
26、to achieve 10% demand. Tests were performed again with balanced flow rates. All circulators were proportionally balanced to their design flow rates. Again, the system was tested with demands of loo%, 70%, 30%, and 10% flow. Total system flow dropped to 53.3 gpm, equal to that of the unbalanced 100%
27、demand with five springfive swing check valves, but total power increased slightly to 1578 watts, an increase of 21 watts over the unbal- anced demand. Flow at 70% demand (seven circulators in operation) decreased to 47.2 gpm but individual pump flow rates have increased. This was expected due to de
28、creased system head loss as a result of lower flow rates. At lower head losses, individual circulators are able to deliver more flow. Power consumption dropped from 1578 watts at 100% Power Consumption vs. Total System Flow Figure 5 Flow vs. demand for individual circulator pump system. demand to 11
29、49 watts at 70% demand. At 30% demand, system flow decreased to 28.3 gpm while individual circulator flows increased again, as expected. For 30% demand, total power consumption dropped to 5 16 watts. System flow rate for 10% demand was 8.7 gpm while system power demand was 195 watts when pump P-1 wa
30、s tested. For 10% demand, only one pump is in operation. Similar results were recorded for other circulators chosen to operate as the 10% demand pump. Again, individual circulator flows increased as system demand dropped. Figure 4 is a flow rate comparison of three pumps, P-2, P- 5, and P-8, in the
31、system that was tested during all system demands of loo%, IO%, 30%, and 10%. As statedbefore, each individual circulator flow rate increased with decreasing system demand as a result of lower system head losses due to lower system demand flow rates. Figure 5 represents the system power consumption v
32、s. the system flow rate for the balanced circulator system as tested at loo%, 70%, 30%, and 10% demand, which represent each of the test points. Note that there is very little difference in the system performance between unbalanced and balanced circu- lators, and there is little difference between t
33、he use of a combi- nation of swing and spring check valves (the middle curve on Figure 5) and the use of all swing check valves. The flow rate was regulated by turning circulators “On” and “Off.” Valves were not adjusted to regulate flow at this time. There was a drastic increase in power demand bet
34、ween 70% and 100% flow demand with only a marginal increase in flow rate. Multiple Circulator Pumps in a Subcentral Piping Network Figure 4 indicates there is a rather large variation in flow through each circulator when total system flow is 100% compared to 10%. This may be unacceptable in many app
35、li- cations. To determine if this occurred in smaller systems with fewer circulators a series of test were performed with fewer ASH RAE Transactions: Symposia 545 Balanced Flow Rates at Various Demands (Loopl: 100%. 75%,5096.25%) 12 -, P-1 P-2 P3 Figure 6 Circulator flow rates at vai percentages-fou
36、r-pump system. P4 DUS system load units. This involved manually closing ball valves to water coils WC-5 through WC-10. This created a loop consisting of four water coils and, thus, four circulator pumps. This system was labeled Loop-1. A second system was created by manually isolating water coils WC
37、-1 through WC-4 and WC-9 and WC- 10. This second system was labeled Loop-2. Each system was tested in the unbalanced and balanced configurations. Flow was regulated by turning circulators “On” and “Off.” Total system flow for all pumps in Loop-1, P-1 through P-4, was 35.2 gpm, which produced a power
38、 consumption of 699 watts. Each circulator pumps results have been graphed in Figure 6 for each of the flow demands in Loop-1. Pump P- 2 was turned off in order to achieve 75% demand. Total system flow dropped to 29.1 gpm, but individual circulator flows slightly increased, which again was expected.
39、 Total system power dropped to 550 watts. Pumps P-2 and P-3 were turned off to achieve 50% demand. Total system flow dropped to 21 gpm, but again the individual circulator flows increased. Total system power dropped to 369 watts. Pumps P-2, P-3, and P-4 were turned off to achieve 25% flow demand. To
40、tal system flow dropped to 9.3 gpm. Total system power decreased to 196 watts. Each circulator pump was tested at 25% demand and is included in the results shown in Figure 6. Pump P-2 was not tested at 75% and 50% system demands and pump P-3 was not tested at 50% system demand. All individual circul
41、ator flows decreased for system flows of 25% demand when compared to system flows at 50% demand. When the loo%, 75%, and 50% bars are compared, flow rates decreased with increasing system demand. Because of this, it was expected that the 25% demand would result with higher flow rates than the 50% de
42、mand. SYSTEM TESTS WITH CONSTANT-SPEED CENTRAL PUMP Once all testing of the circulator pumps was completed, each circulator was removed and replaced with a straight section of pipe. The central pump was then installed where a II Centrai Pump Figure 7 Central pump station with instrumentation. straig
43、ht section of pipe was used during circulator testing, as shown in Figure 7. The system was again pressurized and flushed to remove air and particulates. This required opening all valves, which gave an opportunity to test the central pump in the unbalanced flow operation before testing of the balanc
44、ed system. Test ports were located according to recom- mendations found in the Pump Handbook (2001). A separate power source was supplied to the central pump due to three-phase service requirements of the pump. The circulators only required single-phase service. Figure 7 shows the power supply to th
45、e central pump as it passes through the frequency drive. The initial tests of the central pump were performed without the frequency drive, which could easily be unplugged from the system and bypassed. The test box located at the center of Figure 7 consisted of an accessible panel through which each
46、phase could be accessed. This arrange- ment permitted the use of a true RMS power analyzer or a clamp-on handheld power meter to measure the power of each individual phase to collectively determine the total power consumption of the central pump. The induction clamp-on meter agreed well with the ana
47、lyzer when measuring power with or without the variable-speed drive. Thus the clamp-on meter was used because of its convenience in all test cases concerning the central pump. A pump performance curve was generated for the central pump with and without the frequency drive. This curve is shown in Fig
48、ure 8 along with the manufacturers curve (ITTC 1995). All valves in the system were fully open. The frequency drive was run at 60 Hz and flow was regulated with the drive and without the drive by closing a gate valve at the flat plate heat exchanger, which regulated the system flow. Note that the he
49、ad vs. flow performance of the pump had negligible effect from the presence of the drive when running at 60 Hz. Also note that at maximum flow, the power consumption remained the same at 1390 watts. Efficiency of the pump/motor/drive system increased from 40.6% with the frequency drive to 42.6% when a drive was not used. The system efficiency was 546 ASHRAE Transactions: Symposia Central Pump Power Curves wl Frequency Drlve 1600 1 I l I O 15 30 45 60 75 O 10 20 30 40 50 60 70 Flow Rate (gpm) Flow Rate (gpm) Figure 8 Pump curves from test results at 60 hz and from manufacturer S data. Figur
