12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaFig. 4 Time delay for external bypass (PTC2+P), when tapping is performed just before expected start of by-pass flow, seton 35 °C.In case, when tapping of DHW was performed afterlong idling just after by-pass flow was stopped, timedelay decreased to 8,5 and 16,5 seconds. In thismeasurement, temperature of substation and thuswater standing in the HEX was little higher thanambient air temperature. It is expected that time delaywill be slightly longer, if substation will have realambient temperature but still shorter than in case 2.We also performed measurement of tap delay fiveminutes after previous DHW tapping was finished.In this case, tap delay in substation to produce DHWwith temperature 42 °C and 47 °C was shorter, 7 and14 seconds.For room temperature around 22 °C, external by-passwas opened roughly every 30 minutes. The by-passwas in average opened 2.5 minute and volume of DHwater needed to close the by-pass was in average 3 L,i.e. when substation is idle, by-pass uses 6 L of DHwater per hour.Table 3 – Temperatures measured for PTC2+P controller in first 10 sec after tapping was started for situation after longidling, just before by-pass was expected to run again(sec) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17T22 (°C) 21.6 22.3 26.0 29.7 32.6 35.0 36.9 38.7 39.9 41.2 42.2 42.8 43.5 44.2 44.7 45.1 45.5Time delay in IHEU equipped with IHPT controller withinternal by-pass adjusted by requirement of DHW to47 °C was 6 and 14 seconds to reach 42 °C and 47 °Con outlet for situation when tapping was performed justbefore by-pass was expected to open. The internal bypassopens 3 minutes after previous tapping is finishedand when is once opened never closes, only whenanother tapping is performed, but again only on3 minutes.Table 4 – Overview of time delays for all measured casesThe average flow of internal by-pass was 24 L/hourand average return temperature to DH network was45 °C. When internal by-pass is once opened, the timedelay in substation decrease substantially to 1.5 and7 seconds to produce DHW with temperature 42 °Cand 47 °C. The condition with expected longest timedelay was solution without by pass. In this case timedelay to produce DHW with temperature 42 °C and47 °C was 12 and 25 sec. All measured results aresummarized in Table 4.NO BYPASSEXTERNALBY-PASSINTERNALBY-PASScase number and descriptionT 11(°C)τ 42(sec)τ 45(sec)τ 47(sec)T 12(°C)T 12AVG(°C)T HEX-UP(°C)T HEX-DOWN(°C)1 – after long idling, no by-pass (BYP)50.1 12 18 25 16.2 19.5 20.4 212 – after long idling, just before BYP wasexpected to open again49.6 11 16 22 30.1 19.3 21.5 21.43 – after long idling, just after BYP closed 50.6 8.5 12 16.5 42.6 19 29 264 – 5 minutes after previous tapping finished 50.8 7 10 14 25 19.1 22.3 37.45 – just before BYP was expected to open (3min after prev. tapp. finished))50.5 6 10 14 19.5 19.1 22.6 386 – anytime, when BYP was already inoperation49.3 1.5 3.5 7 47.3 18.4 44 45.566