The Purpose of a Mixing Tank

The addition of the tank is not to provide more storage, after all, the main underground loop has plenty of storage. Rather, the storage tank acts as a mixing tank between the boiler and the main loop.

The following illustration depicts the set up with a typical Ray pack modulating boiler. Water continually circulates through the boiler and temperature is controlled by a mechanical device in the gas valve. A liquid filled sensor located on the hot water side of the boiler shrinks as the water gets cooler and that allows more gas to flow to the burners and increases the flame. As the water becomes hotter, the liquid in the sensor expands and reduces the flow of gas so the flame is reduced. In this way water changes temperature gradually and there is no need for the mixing tank.

The down side to this method is:

1. It is not a precise method of temperature control (temperatures can fluctuate 10^o to 20^o).
2. Delivery temperatures tend to be their hottest at periods low consumption.
3. Boilers tend to be oversized to cover peak periods of consumption.

EDC Technologies controls the boiler electronically. In the second illustration with the storage (mixing) tank there is a separate circulation loop between the tank and the boiler with its own pump. The water is constantly circulating between the tank and the boiler so that the tank stays mixed. Our sensors are located on the ‘hot out’ side of the tank instead of the boiler. When the temperature drops just one degree off programmed temperature we will light the boiler and it will stay on until the whole tank (80-115 gallons) is brought up one degree - then shuts off.

The benefit of this method is that it allows more precise temperature controls at both the boiler and the mixing tank providing tenants adequate hot water with tremendous energy savings.

Additional Benefits:

• System wide diagnostics are possible
• Increased storage for peak period demand
• Lower boiler operating temperatures
• Control of Legionella
• Reduced boiler size
• Reduced boiler replacement cost
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• It is important to note that the addition of the storage tank will make the hot water system more efficient without an EDC Control. Bottom line... It is a good investment for the hot water system. Typical savings from a mixing tank and aqua-stat combination can provide 5-15% savings.