DWHR Testing at the CCHT. ACE 3 Hot Water Forum Pacific Grove, California 9 June 2009 John Gusdorf

Transcription

1 DWHR Testing at the CCHT ACE 3 Hot Water Forum Pacific Grove, California 9 June 2009 John Gusdorf

2 Drain Water Heat Recovery Passive technology to recover heat from drain water Thanks to Chris James for the diagram

3 DWHR Double-wallvented heat exchangers Works on principle that liquid flowing through a vertical pipe flows as film on surface

4 Construction 3-inch (76.2 mm) copper drain pipe, wrapped with either ½ -inch (12.7 mm) or 3/8-inch (9.5 mm) soft copper tubing. The tubing is squared to give more contact area with the pipe. Distinguishes different manufactures

5 Device Configurations Single pass Series Parallel

6 Plumbing configurations Preheated water to hot water tank inlet only Preheated water to hot water tank inlet and cold water to shower.

7 Testing at the Canadian Centre for Housing Technology Done in two phases: Phase I, 2005: Natural gas savings for 4 daily water use patterns Effectiveness of units Maximum shower times Phase II, 2006: Characterize 6 devices in terms of effectiveness & NTU Develop standard testing and modeling methods

8 Phase I, Objectives: Measure the daily natural gas savings from various DWHR devices, in 2 plumbing configurations, with 4 daily schedules of hot & cold water draws. Determine whether non-simultaneous water draws matter Determine the effectiveness of various DWHR devices

9 Phase I, Set-up: Programmed hot & cold water draws through toilet, sink, bath, shower, and simulated dishwasher and clothes washer.

10 The Dishwasher & Washing Machine

11 Phase I: Water Draw Schedules

12 For each device and each schedule Daily gas use was measured Without the DWHR device (The Benchmark) In Configuration A (water from DHWH to DHW tank only), and In Configuration B (water from DWHR to DHW tank and shower cold water)

13 Phase I: Results For the three 60 inch (1527 mm) units tested: Natural gas savings varied from to m 3 /day, and from 9% to 27%. With minor one exception, savings were higher in Configuration B, with greater flow of cold water through the DWHR. The 3 units had very similar average savings: 0.37 to 0.39 m 3 /day, 15.5% to 16.8%

14 Phase I: Non-simultaneous flows Only during the showers and sink draws did warm drain water and cold fresh water flow through a DWHR simultaneously. Gas savings could not be detected for any draws other than showers. This result was not expected. Sink draws and the dishwasher were expected to show minor savings.

15 Phase I: Problem Cold water temperature was not controlled. City water temperature varied from19.3 C on 1 Sept to 9.5 on 5 Feb. Benchmarks were repeated just before or after tests, some were redone. Difference between benchmarks and tests usually <0.5 C, always 2.3 C. But results were affected by different temperatures

16 Phase I: Long showers Flow through showers only to determine in situ effectiveness ε All ε tests took place during 2 days, and cold water varied from 10.2 C to 11.1 C. Flow rates varied from 7.9 to 8.1 L/s. So neither temperature nor flow rates varied significantly. Shower temperature: 46 C (115 F).

17 Phase I: ε Also calculated ε/m and ε/kg. Both relate to price, and longer units won t fit in all locations.

18 Phase I: ε Results Effectiveness varied from 0.67 in a 60- inch unit in Config A to 0.40 in a 36-inch unit in Config B. For a given unit, ε is always higher in Config A. ε/m: 0.59 in a 40 unit to 0.3 in a 60 ε/kg: in a 36 unit to in a 60 Shorter units do better in ε/*.

19 Phase I: Maximum shower lengths The length of time before the shower temperature dropped below body temperature (37.0 C). A relative rating of DWHR devices. Also dependent on HWT, hot and cold temperatures, and flow rate.

20 Phase I: Shower length results With no DWHR: 28 minutes With DWHR: From 39 minutes with a 36 unit in Config A, to >>75 minutes with a 60 unit in Config B. Generally, longer showers with longer units. Always longer showers with Config B.

21 Phase I: Pressure drops Pressure drops may be a problem with pumped well water. ΔP was measured with manual meters. Among the 60 units, ΔP was lowest for the unit with parallel windings, highest for series windings.

22 Phase I: Conclusions DWHR has significant potential to reduce energy use for hot water for showers. Performance of units seems to vary significantly with length, and configuration and squareness of windings. Due to uncontrolled water temperatures, these results should not be used to compare units.

23 Phase II Controlled cold water temperature at 8 C (46 F), the Canadian average. Pressure transducers were added for more accurate ΔP measurements. Only used shower tests to determine NTU and effectiveness of each unit.

24 Phase II: Cold water temperature A 2 kw chiller was used to cool two tanks of 150 and 151 L (~40 US Gal each). A test was started once the two tanks were cooled.

25 Phase II: Calculating ε Was done by logarithmic mean temperature difference and NTU effectiveness. NTU method found to be more appropriate because it does not require exit temperatures.

26 Phase II: Tests for effectiveness Originally 18 tests were planned for each unit: 3 flow rates (6.5, 8.5 & 10.5 L/min) x 3 temperatures (37, 41 & 45 C) x 2 configurations (A & B). After analyzing results for two units, temperature and configuration were shown to be irrelevant. Tests were then done with 8 flow rates from 4 to 10.5 L/min.

27 Phase II: Results NTU vs. Flow

28 Phase II: ε vs. Flow

29 NTU & ε: Highest to lowest PowerPipe 60 GFX 60 GFX 40 Retherm 60 Retherm 40 No name 60 PowerPipe 36 No name 36

30 Phase II: ε/foot

31 Phase II: Pressure Drop Models with parallel and series windings had lower ΔP and lower ΔP/m than those with single windings.

32 Phase II: Calculated Annual Savings

33 Outcomes: The on-line calculator

34 Outcomes: ecoenergy incentives C$95 for models with efficiency from 30% to 41.9% C$165 for models with efficiency of 42% or more.

35 Lower efficiency models

36 Higher efficiency models

37 ecoenergy grants for DWHR 76 out of 108,665 grants of all types. Reasons for low uptake so far: Not suitable for all households, only those with frequent showers Not suitable for houses with slab on grade, crawl space or >1 plumbing stack People don t believe the savings People are afraid to touch the plumbing stack

38 DWHR Pros, Cons & Issues Simple, safe, no maintenance, long life Reasonable price & payback Only good for the right houses & households Questionable for builders of new houses We don t have a model that combines DWHR & SDHW. But we re working on it.

39 Thank you