MAGNA3 & TPE Control Modes

by Reece Robinson, Training & Technical Content Specialist, CBS, Grundfos

A frequently asked question we hear from our partners is, “When should I use other control modes besides AUTOADAPT?”

The AUTOADAPT control mode has an aggressive approach on energy savings. For hydronic closed loop systems using pressure as the control parameter, this is the most energy efficient control mode available on MAGNA3 or TPE3 pumps. When AUTOADAPT is selected, the default setpoint is 50% of the maximum head of the pump.

Example: If the maximum head for that pump is 80 feet (Hmax), the default setpoint (Hset) will be 40 feet at full speed as shown in Figure 1. As the flow is reduced, the pump head will be reduced to the default minimum of 5 feet (Hmin). For many heating and cooling systems this head may be too low to provide sufficient flow to fan coils or other heat transfer elements.

So, what’s the next best choice?

The Proportional Pressure control mode allows for higher head at low flow. Systems that have balancing and/or control valves will require a higher pump head at lower flow rates. There is no default setpoint for Proportional Pressure and must be configured during commissioning. If there is a pump schedule in the construction documents, the pump head can be a starting point. The default setting for head at zero flow (Hmin) is 50% of the setpoint.

Example: Figure 1 shows the middle curve at a setpoint of 40 feet will result in a zero-flow setting of 20 feet. Proportional Pressure (Hmin) and the setpoint (Hmax) can be adjusted to more closely match the installation requirements. Although the setting is called Proportional, which is a linear function shown with a dashed line, this setting can be set to quadratic, as shown with the solid blue curve going from Hset to Hmin.

If Proportional Pressure still does not provide enough head at lower flow rates to satisfy all the coils or heat transfer elements, then select Constant Differential Pressure as the control mode. This will result in a setpoint that remains constant at all flow rates. There are some hydronic systems that will have a high head requirement at low flow because the friction losses in the distribution piping are lower than the control valve losses. This will balance the valves and coils.

It can be difficult to know the head loss characteristics in retrofit situations if replacing an existing pump. If control and balancing valves are not present, start with AUTOADAPT. This will be the most energy efficient solution. If that doesn’t work, then start with Proportional Pressure at the lowest minimum head at zero flow and work your way up. The end user will have one of the most efficient circulators available on the market today.