As those of you who use the Heatlink Radiant Heating System know, the systems are typically designed using a simple injection-mixing valve. By designing for one system temperature and varying the flow, we keep things simple.
The above being said, I recognize that many people are looking to use variable speed injection pumping to supply the system water. A recent article in the Radiant Living magazine by John Siegenthaler, addresses other requirements of a variable speed mixing design that must be considered if you are to give your customer an optimum system.
Several pump manufacturers make small pumps suitable for variable speed operation. However, simply installing the pump without calculating the necessary injection flow rate and combining that with a properly calibrated balancing valve will being doing your customer a disservice. Mr. Siegenthaler offers mathematical equations to be used in properly calculating the flow requirements to the radiant and also the cv setting for the balancing valve.
Knowledge is a wonderful thing!