STEAM, HOT AND DOMESTIC WATER CIRCULATION SYSTEM:

Note: Sensor data is currently unavailable for this system. However, we are working on publishing this data to the web. For questions on the progress of this project, please contact the ITLL Staff.

General Description
Operation
Technical Specifications

General Description

Heat Exchanger

The heat exchanger uses steam from the campus boiler to heat water for use in various heating coils throughout the building. The heating water is circulated by heating water pumps to heating coils in the cabinet unit heaters, fintube radiators and reheat coils in the zone variable air volume boxes.

On cold days, room temperatures (especially those rooms with windows and outside walls) drop. The room thermostats send this information to the main control system. If the room temperature cannot be brought back up by reducing the cool air supply from the duct, then the hot water flow to the heating coil in the VAV box is increased.
As the duct supply air flows ( through VAV-41) past the coil, the room is heated, and the hot water is cooled.
The temperature of the water () exiting the heat exchanger drops, and a thermocouple sensing this change signals a valve to automatically increase the steam flow until the temperature of water leaving the heat exchanger rises to a preset value ().

 

[Domestic Water Heating System]
The shell-and-tube type heat exchanger also uses low-pressure steam () from the campus boiler to heat water for domestic use
(); i.e., for hot water in restrooms, etc.
As people use hot water from faucets, for example, colder city water enters the system to replace it. This drops the temperature of the water circulating in the domestic hot water loop. A thermocouple at the exit of the heat exchanger senses this drop and signals the steam valve to increase the steam
,
to maintain the water temperature leaving the heat exchanger (approximately 140°F or 60°C).




Heating Water Pump (HWP-1&2)

The heating water pumps circulate water through heat exchanger HX-1 and then to heating coils in the cabinet unit heaters, fintube radiators and reheat coils in the zone variable air volume boxes.

The pumps are of the constant-speed centrifugal type. An air separator (AS-1) on the pump return line eliminates air from the heating water, while an expansion tank (ET-2) prevents system over-pressurization as the system's temperature changes. Also, the ET-2 provides a pressure reference point for the system to insure sufficient suction pressure to the pump, preventing cavitation.

Heating water pumps 1 & 2 operate continuously and in parallel.

Operation

Heat Exchangers

The direct digital control (DDC) system controls the steam valves () supplying the heat exchanger to maintain supply water temperature inversely proportional to the outside air
(OAT).

For an OAT of 10°F (-12.22°C) or lower, the supply water temperature setpoint is 180°F (82.22°C); for an OAT of 60°F (15.55°C) or higher, the supply water temperature setpoint is 100°F (37.77°C). Between these outside temperatures, the supply water temperature varies linearly between 180°F (82.22°C) and 100°F (37.77°C).

To prevent overheating the heat exchanger, the steam valves do not open at all unless the water flow switch indicates water flow.


Heating Water Pumps (HWP-1 & 2) - Control

If the outside air temperature is below 65°F (18.33°C), the heating water pumps run continuously; above 68°F (20°C), the pumps are de-energized.

Unless one pump requires maintenance, the heating water pumps run simultaneously at all times.



Specifications


Heat Exchanger-1

Plan Symbol

HX-1

Submittal Ref. #

15755

Location

00-34

Manufacturer

Taco

Supplier

McLemore Pump, Inc., 371-5730

Type

Multi-pass shell and tube

Model No.

WS8-60-2A

Size

8

Service

Steam to water heat exchange

Design Steam Pressure

15 psig

Design Sat. Steam Temp.

249.8°F

Design Steam Flow

2068.9 lb / hr

LMTD

88.3

Design Water Flow Rate

100 gpm

Ent. Water Temp.

140°F

Leaving Water Temp.

180°F

Tubeside (water) Vel.

4.02 ft / s

Tubeside Press. Drop

1.95 ft WC

Fouling Factor

0.0005

Load

1,956,350 Btu / hr

Shell / Head Material

Steel / Cast Iron

Tube Size / Thickness

3/4" x 20 BGW Copper / 0.035 in. wall

Tubeside Working Press.

150 psig

Shellside Working Press.

150 psig

Maximum Temperature

375°F


Heat Exchanger-2

Plan Symbol

HX-2

Submittal Ref. #

15755

Location

00-34

Manufacturer

Taco

Supplier

McLemore Pump, Inc., 371-5730

Type

Multi-pass shell and tube

Model No.

WS-36-2A-DW

Size

6"

Service

Steam to water heat exchange

Design Steam Pressure

15 psig

Design Sat. Steam Temp.

249.8°F

Design Steam Flow

921.2 lb / hr

LMTD

172.4

Design Water Flow Rate

25 gpm

Ent. Water Temp.

40ݔF

Leaving Water Temp.

110°F

Tubeside (water) Vel.

3.82 ft / s

Tubeside Press. Drop

0.83 ft WC

Fouling Factor

0.0005

Load

871,140 Btu / hr

Shell / Head Material

Steel / Cast Iron

Tube Size / Thickness

3/4" x 20 Double Wall Copper / 0.047 in. double wall

Tubeside Working Press.

150 psig

Shellside Working Press.

150 psig

Maximum Temperature

375°F



Heating Water Pump

Plan Symbol

HWP-1&2

Submittal Ref. #

15160

Location

Mechanical Room

Manufacturer

Aurora Pump

Supplier

McLemore Pump, Inc. 371-5730

Model

411A; 96-12895-2

Size

2 x 2.5 x 7.5

Service

Heating Water

Pump Curve No.

2PC-117352

Design Flow Rate

50 gpm

Total Head

55 ft @ design flow rate

Drive Type

Direct (Woods J-type coupling)

Motor Power

3 hp

Motor RPM

1750

Motor Voltage

460 V, 3ph, 60 Hz

Motor Full Load Current

4.8 A (approx)

Motor Frame Size

182T