LEVEL 3 EXTENDED DIPLOMA MECHANICAL AND ELECTRICAL SERVICES CONSTRUCTION BOILER RECOVERY TIMES

MECHANICAL AND ELECTRICAL SERVICES IN CONSTRUCTION AIMS TO UNDERSTAND THE PROCESS OF CALCULATING THE TIME TAKEN FOR A BOILER TO REHEAT COLD WATER. OBJECTIVES TO UNDERSTAND THE TERMS OF HOT WATER HEATING. TO INVESTIGATE THE HOT WATER SYSTEM IN A DOMESTIC SITUATION. TO COMPLETE A CALCULATION BASED ON A DOMESTIC HOT WATER SYSTEM.

MECHANICAL AND ELECTRICAL SERVICES IN CONSTRUCTION WITH ANY HOT WATER SYSTEM, THE SIZE OF THE BOILER IS BASED ON THE NUMBER OF PEOPLE, AND THE BUILDING ARRANGEMENT AS TO ITS SIZE AND PERFORMANCE. IN ADDITION THE CAPACITY OF ANY HOT WATER STORAGE VESSEL MUST ALSO BE ABLE TO MEET THE REQUIREMENTS OF THE BUILDING. TWO IMPORTANT CONSIDERATIONS FOR ANY HEATING SYSTEM IS THE RATE OF ENERGY CONSUMPTION, (MEASURED IN KILO WATT / PERSON) AND THE TIME IT TAKES FOR A SYSTEM TO REHEAT THE WATER. A GOOD EXAMPLE OF THIS IS TO CALCULATE THE TIME IT TAKES A HOT WATER SYSTEM TO REHEAT THE WATER, AFTER YOU HAVE JUST FILLED THE BATH.

MECHANICAL AND ELECTRICAL SERVICES IN CONSTRUCTION

IN OUR FIRST EXAMPLE WE TALKED ABOUT A LARGE DOMESTIC PROPERTY AND CALCULATED A PIPE SIZE OF 35MM FOR THE HOT WATER SYSTEM. IF THIS LARGE DOMESTIC PROPERTY HAD 5 BEDROOMS AND TWO BATHROOMS, A HOT WATER SYSTEM THAT WAS SUPPLIED BY A 30KW BOILER, HOW LONG WOULD IT TAKE TO REHEAT THE SYSTEM IF THE BATH HAD BEEN FILLED WITH HOT WATER? THE FORMULA WE WOULD USE IS BOILER POWER = KGS OF WATER X SHCX TEMP RISE TIME IN SECONDS HOWEVER WE NEED TO TRANSPOSE THIS FORMULA FOR TIME

MECHANICAL AND ELECTRICAL SERVICES IN CONSTRUCTION TIME IN SECONDS = KGS OF WATER X SHC X TEMP RISE BOILER POWER KGS OF WATER = FROM THE TABLE WE IDENTIFY THE STORAGE CAPACITY FOR THE NUMBER OF PEOPLE LIVING IN THE HOUSE. FOR THIS CALCULATION WE WILL ASSUME THERE ARE 6 PEOPLE IN THE HOUSE. SHC = SPECIFIC HEAT CAPACITY OF WATER 4.2 KJ/KGK TEMP RISE. = WHAT DO WE WANT THE TEMPERATURE TO BE (60°C) – THE TEMPERATURE OF THE COLD WATER REFILLING THE CYLINDER. (IN SUMMER THIS MAYBE 15°C OR IN WINTER IT COULD DROP TO 5°C. THE BOILER POWER FOR THIS EXAMPLE WE HAVE ALREADY IDENTIFIED AS 30KW.

MECHANICAL AND ELECTRICAL SERVICES IN CONSTRUCTION TIME IN SECONDS = KGS OF WATER X SHC X TEMP RISE BOILER POWER TIME IN SECONDS = (6 X 45 ) X 4.2 X (60 – 15) 30 TIME IN SECONDS = 270 X 4.2 X TIME IN SECONDS = TIME IN SECONDS = 1701 (HOWEVER WE NEED TO CONVERT THIS FROM SECONDS TO MINUTES BY DIVIDING BY 60) TIME = 1701 ÷ 60 = MINUTES (29 MINS)

MECHANICAL AND ELECTRICAL SERVICES IN CONSTRUCTION TIME IN SECONDS = KGS OF WATER X SHC X TEMP RISE BOILER POWER TIME IN SECONDS = (6 X 45 ) X 4.2 X (60 – 5) 30 TIME IN SECONDS = 270 X 4.2 X TIME IN SECONDS = TIME IN SECONDS = 2079 TIME = MINUTES (35 MINS)

MECHANICAL AND ELECTRICAL SERVICES IN CONSTRUCTION SO HOW COULD WE SPEED UP THIS PROCESS AND MAKE THE HOT WATER SYSTEM HEAT UP QUICKER THAN 29 (SUMMER) AND 35 (WINTER) MINUTES. INSTALL A BIGGER BOILER. SO HAVE A GO AT USING A 40KW BOILER IN THE SAME SYSTEM AND CALCULATE HOW MUCH QUICKER THE SYSTEM WOULD HEAT UP.

MECHANICAL AND ELECTRICAL SERVICES IN CONSTRUCTION TIME IN SECONDS = KGS OF WATER X SHC X TEMP RISE BOILER POWER TIME IN SECONDS = (6 X 45 ) X 4.2 X (60 – 15) 40 TIME IN SECONDS = 270 X 4.2 X TIME IN SECONDS = TIME IN SECONDS = (÷ 60) TIME = MINS. (SUMMER)

MECHANICAL AND ELECTRICAL SERVICES IN CONSTRUCTION TIME IN SECONDS = KGS OF WATER X SHC X TEMP RISE BOILER POWER TIME IN SECONDS = (6 X 45 ) X 4.2 X (60 – 5) 40 TIME IN SECONDS = 270 X 4.2 X TIME IN SECONDS = TIME IN SECONDS = (÷ 60) TIME = 26 MINS. (WINTER)