This depends upon pipe size and flow rates. The most economical solution for flow rates up to 2.5m3/hr is to use the all in one in line compact heat meters.
For larger sizes use a multi jet or Woltmann hot water meter (or a cold meter for chilled water applications) in conjunction with a wall mounted heat meter. Also, 2 temperature pockets must be used, one for flow and the other for return. The 85mm version size pocket is preferred for all pipe sizes. The water meter should be fitted in the return flow and the pulsed output connects into the heat meter to give the flow information.