[I sent this message with 2 itty-bitty photos attached. It probably bounced.]
Okay. I did some rudimentary tests with thermocouples taped to the outside of flexible braided 1/2 inch pipes under my bathroom sink. I can supply the gory details if anyone is interested. Summary: I measured in the evening from 8:42 to 10:19 p.m., and again in the morning from 8:00 to 8:31 a.m. I used an Omega HH12B dual probe thermocouple and two red liquid thermometers. See: http://www.omega.com/pptst/HH11B.html I taped two probes to the outside of the hot water pipe, with plastic Band-Aids, then covered them with foam pipe insulation. This is a crude method. Rossi's insulated tape is better. I measured the water temperature as it flowed into the sink using a red liquid thermometer. These pipes are well insulated. Much better than copper or steel pipes. The difference between the water temperature and the pipe surface temperature was typically around 7°C. There is a surprisingly large difference in temperature from one location on the pipe to the other. It ranges from ~2.4 to ~3.0°C. Where the T2 probe was taped, I tied the hot water pipe and cold water pipe together with string, wrapped them in shipping tape, and then wrapped the whole thing in foam pipe insulation. [DO NOT SEE the two photos NOT attached.] T1 is higher up on the pipe, T2 is below, where the pipes are tied together. T1 heated up faster and remained persistently warmer. The T2 probe is on the side opposite the cold water pipe. Tying the pipes together and insulating them together made no measurable difference to the temperature registered at the T2 location. I think I can measure a difference here of ~0.2°C. There was no measurable difference between these three situations: With hot water running -- 1. T2 location by itself (not tied to the cold water pipe) 2. T2 tied to the cold water pipe, no cold water flowing 3. T2 tied to cold water pipe with cold water flowing With hot water off, cold water running, after a night of cooling-- 4. T2 tied to cold water pipe. A slight change of ~0.1°C may have registered after 5 min. The cold water was 16°C, ambient 18°C. With no water flowing T1-T2 was initially ~0.0°C ~0.1°C (a bias) and after 5 min. of cold water it occasionally registered 0.2°C. This arrangement was rather noisy because of changes in the hot water temperature. These were more rapid than I expected they would be. I ended up using the MIN/MAX feature for 5-minute segments. In most cases I compared T1 to T2, which eliminates the effect of hot water temperature changes. I also compared T2 to itself over 5 minute segments. I did this with and without cold water flowing. In some cases I zeroed out the difference with the REL key before starting 5 minute measurements. - Jed
