3.2 Flashcards
found in many medium and large commercial buildings; rare in some residences;
continuously circulates hot water from the water-heating unit back to the water heater;
ensures that hot water is always available at the taps; avoiding the need to run water for a long time to obtain water at the desired temperature.
hot water recirculating systems
water is constantly recirculated from the water heater through the piping;
best for buildings who always have occupancy throughout the day;
examples are hospitalsand multiunit residentialbuildings……
continuous recirculating
uses an electronic or electro-mechanical timer to shut off circulation of hot water when there are no occupants;
examples are commercial, institutional,and industrial buildingsthat are closed atnight/weekends.
timed recirculating
relies on a sensor located at a remote location in the recirculating line;
this sensor senses water temperature and activates there circulating pump when water temperature drops below the settemperature.
thermostatically controlled recirculating
DETERMINING WATER HEATER SIZE
A water heating system must be designed to have sufficient capacity to provide hot water during periods of peak use. An accepted method of determining the maximum demand on a waterheateris to determine __________ during aparticular time of day. For single- and two-family dwelling units, this peak occurs during the morning or early evening.
Determining Water Heater Size, peak usage
SIZING STORAGE TANK WATER HEATERS
Residential water heaters are typically sized based on their ____________________. This is the sum of the “standby” hot water found inthe tank plus the capacity of the heater to heat water during that first hour.
first hour rating (FHR)
SIZING STORAGE TANK WATER HEATERS
Typically, standby water is taken as _____% of the tank capacity. Theamount of water in the tank is multiplied by ____ percent because aswater is being used, new cold water is entering the tank and diluting some of the heated water.
70
SIZING STORAGE TANK WATER HEATERS
A common residential electric water heater is rated at ________ to ________ watts, which would be a recovery rate of about ____ to ____ gallon per hour.
The recovery rate of a gas-fired water heater is typically about ___________ the rate of electric-powered units having the same storage tank size. To compensate and provide a suitable FHR, electric water heater storage tanks are typically larger.
In sizing a storage tank-type water heater, the _____ of a water heater must meet or exceed the peak hot water demand.
3000, 4500, 12, 18, double, FHR
SIZING INSTANTANEOUS WATER HEATERS
____________________________ are selected based on the amountof hot water needed to meet the ________ (peak instantaneous demand), in gpm or L/min, at a specific water temperature rise and other criteria. The design load (the flow rate of the instantaneous waterheater) is determined by adding flow rates of fixtures used ______________.
instantaneous water heaters, design load, simultaneously
SIZING INSTANTANEOUS WATER HEATERS
Most instantaneous water heaters are rated for flowrates at a variety of inlet water temperatures or temperature rises. A good assumption in design ofinstantaneous water heaters is that that the incoming potable water temperature is no warmer than ___ °F(10°C). A temperature of ___° to ___°F (2° to 4°C) should be used in cold climates.
50, 35, 40
SIZING INSTANTANEOUS WATER HEATERS
Water must typically be heated to _____°F (49°C) for most residential uses. To determine the required temperature rise needed, subtract the _________ water temperature from the ___________ output temperature. The needed temperature rise is typically at least ___°F (39°C).
120, 70, incoming, desired
SIZING A LARGE MULTIFAMILY WATER HEATING SYSTEM
As with one- and two-family water heaters, a hot water system must be designed to provide a sufficient supply of hot water foruse by building occupants during peak periods of use. In large multifamily dwellings,such as apartments or condominiums with ___ or more units,hotwater demand tends to peak between ___ and ___ AM and again between ___ and ___ PM.
10, 6, 9, 5, 8
SIZING A LARGE MULTIFAMILY WATER HEATING SYSTEM
An __________________ used to determine hot water demand in large multifamily buildings unitsis based on the ____________ (DU). For apartments or condominiums, a DU is counted for each __________ and ___________________ served by the waterheating system.
approximation method , demand unit, bathroom, clothes washing machine
SIZING A LARGE MULTIFAMILY WATER HEATING SYSTEM
For apartments or condominiums with 10 or more units:Max probable demand (MPD) of hot water MPD = ______ + _____ (DU)-meaning ____ gal/hr for each demand unit plus ______ gal/hr reserve capacity.
350, 11, 11, 350
a mechanical device used to move a fluid by converting mechanical energy to pressure energy called head
pumps
used to circulate or pump waer in domestic hot and cold water systems, hydronic ( hot water) and chilled water distribution systems, feed water systems for boilers and chillers, condensate return systems, well systems, wastewater treatment systems, sump installations, and other process piping systems
pumps
TYPES OF PUMPS
are designed to ensure that any pumping action is forward (positive). Its internal design ensures and prevents fluid from recirculating back towards the pump inlet, or within its casing.
Positive Displacement Pump
TYPES OF PUMPS
has an expanding cavity on the suction sideof the pump and a decreasing cavity on thedischarge side.
Positive Displacement Pump
