Small Chilled Water & Radiant Heat Buffer Tanks

High quality stainless steel multi-purpose hydronic system tanks for backup heat, hydraulic separation, buffer, or volume expander, for use in hydronic, radiant, or chiller systems. Robotic-welded stainless steel tank construction is used for both inner and outer tank.

What is a buffer tank?

A buffer tank is used for a small amount of energy storage, and to provide hydraulic separation whereby a pump circulates heated or chilled water into the tank on the source side, and a second pump circulates water out of, and back to the tank, on the load side. In this way, the supply and load pumps don’t “see” each other or cause flow irregularities.

Buffer tanks are often used to “smooth out” the operation of a boiler or chiller to prevent or mitigate cycling. With Chiltrix heat pumps, which are variable speed, short cycling is not an issue however due to Chiltrix’s unique controls; buffer tanks are needed whenever a Chiltrix heat pump interfaces with a radiant or floor loop.

Chiltrix heat pumps include a built-in pump. When used for floor or radiant heating, the Chiltrix controls are designed to maintain a specific temperature in the buffer tank, but they are not designed to circulate water through the floor or radiant loop. Therefore, there must be a means of hydraulic separation such as a buffer tank when using Chiltrix hydronic heat pumps for floor heat or radiant heating. In a Chiltrix heat pump system, an automatic seasonal valve can bypass the tank in cooling mode if desired (when not being used for heating).

Even when a heat pump system is designed to operate without a buffer tank, any such system would still operate better with a buffer tank.

A buffer tank (or buffer vessel) will always have at least 4 water ports, two for the “source side”, a supply and return, and two on the “load side”, a supply and return. A vertical buffer tank is one that stands upright and this design allows strong thermal stratification. In some cases a horizontal buffer tank is needed for space requirements. In the horizontal design, less stratification will occur.

Buffer tanks may be large or small. Chiltrix makes a 19-gallon tank that is well suited for residential and small commercial applications including biomass, fermentation, thermal storage, chiller systems, hydronic heat pumps, hydraulic separation, and use with wood boilers, gas boilers, or other types of hydronic or radiant heating systems that need a small buffer tank. Chiltrix also produces 37 gallon and 58 gallon buffer tanks which are very useful with larger or more complex systems, in particular, when multiple heat pumps and/or load types are combined in a single system.

What is a backup heating tank?

In a hydronic heat pump system, as with any other heat pump, capacity falls when outdoor weather is extremely cold. For customers in cold climates,  and there may be a few days each year that cannot be handled solely by the heat pump, therefore a backup heat source should be available. The simplest and cheapest solution (but not the best) is an electric backup heating element in a tank. Even though electricity may be more costly than natural gas, a gas water heater costs far more to buy and install and since it may be rarely used, the electric tank is a better overall backup heat solution. Further, electricity can be replaced or offset by solar which is not the case with gas. The best and most energy efficient way to provide backup heat to a hydronic system is to use an electric heater inline between the heat pump outlet and a buffer tank inlet that is variably controlled by the heat pump to dynamically inject precise amounts of heat, such as the V18.

What is a volume expander tank?

This is just what it sounds like – a tank that increases the water volume of the overall system. With Chiltrix heat pump chillers, we recommend at least 10-15 gallons of water in the system. For small systems where everything is close to the outdoor unit, a small tank may be needed to make sure that there is enough volume (gallons) in the system. Other than very small systems, Chiltrix only requires a buffer tank for floor or radiant heating operation and the Chiltrix system can automatically activate an optional “seasonal valve” to bypass or isolate the buffer tank when operating in cooling mode. A volume expander tank expands the volume, without buffering, and without using a 2nd load-side pump. However, as mentioned, while heat pump systems can be designed to operate without a buffer tank, any such system will still perform better if it has one.

What is an expansion tank?
Chiltrix does not provide expansion tanks. These are widely available commodity items used to accept extra water (maintains correct pressure as water expands/contracts due to temperature change). The Chiltrix heat pumps include small internal expansion tanks, however you will almost always need an additional expansion tank. The size needed can be calculated after the final system design is complete and the total system volume is known.