2. **Coefficient of Thermal Expansion (β)**: This value depends on the type of glycol solution being used and its concentration. The thermal expansion coefficient for propylene glycol, for example, is approximately 0.0004 per degree Celsius at 20°C. This value increases with temperature.

In conclusion, Solar Drainback Tank Sizing can be a beneficial process, as it helps maximize the efficiency and performance of a household’s solar water heating system. However, it also comes with a significant financial cost, as well as the risk of making a mistake in the sizing process.

The system volume needed to calculate the size of a solar expansion tank in a pressurized glycol solar hot water system is specifically the volume of fluid in the system that is subject to thermal expansion. This will usually include the volume in the solar collectors and the associated piping, up to the location of the expansion tank.

Bell & Gossett

Outdoor ON-DEMAND tankless recirc system. For up to 100 ft. of total pipe length and tankless flow requirement of .4 GPM or less. On-demand switch controlled.

For outdoor tankless installation with a dedicated return line and with LESS than .4 GPM flow requirement. Up to 250 ft. of total pipe length.

Outdoor ON-DEMAND tankless recirc system. For up to 600 ft. of total pipe length and tankless flow requirement of .4 GPM or more. On-demand switch controlled.

1. Calculate the volume of your solar liquid (a mixture of water and glycol). 2. Calculate the thermal expansion of the solar liquid. 3. Factor in the initial and maximum system pressure. 4. Factor in the acceptance factor for the expansion tank.

Outdoor tankless recirc system. For up to 100 ft. of total pipe length and tankless flow requirement of .4 GPM or less. Timer controlled.

Hot waterrecirculatingpumpinstallation diagram

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Size of Expansion Tank = (System Volume x Coefficient of Thermal Expansion x (Max System Temp – Ambient Temp) x Safety Factor) / (Max System Pressure – Initial System Pressure)

Hot watertank

Calculating the size of a solar expansion tank for a pressurized glycol solar hot water system requires understanding various factors related to the thermal expansion of the glycol solution, the characteristics of your system, and the pressures it will face. The steps to determine the right size of expansion tank generally include:

These pumps are typically used in the Southern part of the US market where tankless heaters are installed outside to save on expensive air intake and exhaust systems. Use with tankless heaters without a built-in pump. Single pipe and dedicated return line models. Options include on-demand and timer controls.

WaterHeater

The result will give you the required volume of the expansion tank in liters. Note that the actual size of the tank you purchase should be larger than this because the acceptance factor is less than 1.

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6. **Acceptance Factor (Af)**: This is the ratio of the amount of water the tank can hold compared to the total volume of the tank. For most expansion tanks, this value is usually around 0.5 but can vary depending on the design of the tank.

The exact location of the expansion tank can vary in different systems. In most cases, the expansion tank is typically installed near the solar heat exchanger or the solar storage tank, and on the solar loop side. Any fluid downstream of the expansion tank in the system (such as in the domestic water portion of the system or on the “house” side of a heat exchanger) is typically not subject to the same degree of thermal expansion and thus is not included in the calculations.

For outdoor tankless installation with a dedicated return line and with MORE than .4 GPM flow requirement. Up to 600 ft. of total pipe length.

One of the significant drawbacks of Solar Drainback Tank Sizing is that it can be quite expensive. As different factors must be taken into account when sizing a tank, this process can require a large investment of resources. Additionally, there is always a risk of making a miscalculation, which could result in a tank that is either too big or too small for the households needs.

The primary benefit of Solar Drainback Tank Sizing is that it ensures that the tank is large enough to handle the needs of a household. Proper sizing ensures that a tank can store and release enough hot water to meet the demand of all the household’s hot water needs. Additionally, proper sizing ensures that the system will be as efficient as possible, maximizing the utilization of the solar energy being collected.

Remember that this calculation is an approximation and other factors such as local regulations, manufacturer guidelines, and system dynamics can influence the appropriate size of an expansion tank. It’s always recommended to consult with a professional when designing solar hot water systems.

Solar Drainback Tank Sizing is a process that requires the correct sizing of a solar hot water tank based on the specific needs of a household. The goal of this sizing is to maximize the efficiency of the hot water system and ensure that the tank can provide enough hot water for the household at all times. While this sizing process has numerous advantages, it also comes with several drawbacks.

3. **Max System Temp (Tmax) and Ambient Temp (Tamb)**: Tmax is the maximum temperature the solar liquid can reach during operation. Tamb is the ambient temperature or the starting temperature of the system. These temperatures are often in degrees Celsius.

To determine this volume, you would add the volume of the solar collectors (usually provided by the manufacturer) to the volume of the solar loop piping. The volume of the piping can be calculated using its internal diameter and length. Remember to account for all the piping that connects the solar collectors to the expansion tank.

5. **Max System Pressure (Pmax) and Initial System Pressure (Pinit)**: Pmax is the maximum pressure your system is designed to handle. Pinit is the pressure in the system when it is cold and at rest, before solar heat is applied. These pressures are typically given in bars.

4. **Safety Factor (S)**: This is a factor of safety that’s used to account for unknown or varying conditions. A common value is 1.1 to 1.3, but it may vary based on system design and local regulations.

Suppose you have a system volume of 200 liters and you are using a propylene glycol solution with a thermal expansion coefficient of 0.0004 per degree Celsius at 20°C. Let’s assume the max system temperature is 120°C and the ambient temperature is 20°C. You’re using a safety factor of 1.2. The max system pressure is 6 bars and the initial system pressure is 1 bar.

1. **System Volume (V)**: This is the total volume of liquid in your solar system, including both the piping and the solar collector. This is often determined by the system’s specifications or can be calculated by adding up the volumes of individual system components.