The Idea
When the Water Tower Square complex was used as paper manufacturing plant by C. A. Reed, the large boilers heated the over 300,000 square foot complex. Water Tower Square, LLC decided to implement a new and innovative system to update the heating system and add cooling.
The sewage treatment plant located next door gave the HVAC systems designers and idea; why not use the sewage treatment plants discharge to the river to heat and cool the new office complex? The Williamsport Sanitary Authority was willing to lend its discharge and have its temperature changed a few degrees.
How the System Works
Each 1,000 sq. ft. heating zone in the building has its own system to control temperature. Each zone is about the size of a school classroom. At the present time, there are over 50 zones in the building. There will be over 150 zones when the renovations are complete (with approximately 550 tons of cooling capacity).
Each zone has a heat pump that responds to a thermostat to heat or cool its zone. Each heat pump is connected to a circulating loop of water that either brings heat or takes heat away from the heat pump. When the zone calls for cooling, the heat pump can deliver 55 degree air to its space while raising the water in the loop only a couple of degrees. When the thermostat calls for heat, the heat pump can deliver 112 degree air while lowering the water in the loop only a couple of degrees. The water supplied to each heat pump is constantly circulated by a series of pumps. To keep the circulating loop temperature within its desired operating range, the loop water needs to be cooled in the summer and heated in the winter. The effluent from the sewage plant handles this job.
In the summer, the effluent is about 75 degrees as it goes from the plant to the river. A portion of the effluent is pumped to the building where it passes between a series of stainless steel plates before returning to the river. The water in the inside loop passes on the opposite side of the stainless steel plates. Heat from the inside loop passes through the stainless steel plates to the effluent water that carries it to the river. The temperature of the effluent is raised about 2 degrees. In the winter the temperature of the effluent is in the 50′s, so it can keep the loop from getting below 45 degrees and supply heat to the building. Since the temperatures never go below freezing, ordinary water is used in the system.
Features to Make the System Efficient
To save on energy, only as much water as required by the system is pumped. Each heat pump has a switch that allows water to flow in only on an as-needed basis. Pressure sensors monitor the loop and control the loop pumps. The pumps that deliver effluent to the heat exchangers only operate when they are needed to keep the loop temperature within its preset range. At a time when some areas of the building need heating and others cooling, the HVAC system can balance itself without any additional effluent water.
Outside air is necessary for a healthy indoor environment. Air to air heat exchangers designed into the system to heat the air in the winter and cool it in the summer. By using the air being exhausted from the building, the process becomes less expensive. The exhaust air is passed on one side of metal plates while the incoming air is passed on the other side. This allows the heat to be exchanged while bringing in fresh air. It is the same idea as the water loop heat exchanger, except air rather than water is being used.
Conclusion
The innovation system has been working well for three years. An ongoing energy audit of the entire HVAC operation determines the cost effectiveness and efficiency of the system. Preliminary figures look very good. A sewage treatment plant can be a good neighbor.
