Macalister Hall utilizes hot water for its heating needs and chilled water for its cooling needs. The two systems will be outlined below:
Hot Water Heating:
The hot water for the complex is created through a heat exchanger in the basement of Macalister Hall. A 125 psi high pressure steam line from the city provides the heating medium for this shell and tube heat exchanger. Normally, heating coils in air handling units and fan coil units utilize 180 F water, while reheat coils traditionally use a lower temperature, usually around 140 F. However, upon investigation I did not see two sets of hot water pipes, which would indicate that all heating coils use a single temperature water. My guess is that the heating coils use 180 F water since it offers better heating properties. There are two hot water storage tanks in the basement and two hot water circulation pumps. The hot water travels through a system of pipes to service the heating coils in the air handling units and to serve the reheat coils on each floor. Hot water piping is also used to serve the fan coils located in the tower. A full schematic of the piping system can be seen below with the hot water supply piping shown in a solid pink line and the hot water return shown in a dashed pink line.
Chilled Water Cooling:
The chilled water for the complex is served from a 450 ton chiller located in the Creese penthouse. Originally, two 225 ton chillers served the complex, but this equipment is now dormant. The 450 ton chiller was installed three years ago and runs on HCFC-123 refrigerant. There is a cooling tower located on the Creese roof and two condenser water pumps circulate the condenser water loop. Additionally, the chilled water pump located in the penthouse has a variable speed drive system to allow a part load scenario.
Picture of 450 Ton Chiller in Creese
The chilled water that is produced serves the cooling coils in the air handling units and serves the fan coil units located throughout the tower. A full schematic of the piping system can be seen below with the chilled water supply shown in a solid blue line and the chilled water return shown in a dashed blue line.
Fan Coil Units:
Fan coil units are located throughout the complex, mainly in the tower on an exterior wall. I have deduced that these are four pipe fan coil units since chilled and hot water is available all year long. Additionally, I did not observe any pipes labeled "Dual Temperature" or "Hot/Cold" on my survey, which enforces the idea that the fan coil units are a four pipe system.
Pipe Sizing Chart:
As calculated through the Carrier E-20 program, I found the hot water to require 210 gpm and the chilled water to require 720 gpm. These gpm values do not take into account the load from the fan coil units or other outside sources. From the chart below, I can estimate the minimum size of the chilled water and hot water lines serving Macalister Hall.
ASHRAE Recommended Maximum GPM
From the Carrier E-20 calculations, I found that the chilled water flow rate was 720 gpm and the hot water flow rate was 210 gpm. In large scale applications with high flow rates, steel pipe is normally used. According to the table above, Macalister Hall would require a 6" chilled water service and a 4" hot water service. However, it is important to note that the calculated flow rates do not take the fan coil unit circuit into account. On the chilled water side, we have 55 gpm flexibility, and on the hot water side we have 60 gpm flexibility before being required to move up to the next pipe size.
When evaluating the flow rate of fan coil units, I estimated that a one ton fan coil unit would require 2.5 gpm for cooling and 1.2 gpm for heating. If we assume ten fan coil units on each floor of the tower, this will increase the cooling flow rate by 100 gpm and the heating flow rate by 48 gpm. With these numbers in mind, the adjusted pipe sizes would be:
The flow of water into the coils is controlled by a two way control valve. The control valves throughout the complex are pneumatic. These pneumatic control valves are operated through the manipulation of compressed air, which originates at the air compressor in the basement mechanical room. A two way control valve is preferable to a three way arrangement because it is more energy efficient and does not result in the pressure problems often associated with a three way valve.
Macalister Hall Piping Schematic: