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sure it is it saves 40 to 60 % but there is a limitation for using it, this limitation related to the CFM of the return air it must be more than 60% of supply.
as an example (ASHRAE Systems and Equipment 2008 S25)
Example 3. Sensible Heat Energy Recovery in a Heat Pipe Outside air at 10°C enters a six-row heat pipe with a flow rate of 5 kg/s and a face velocity of 2.5 m/s. Exhaust air enters the heat pipe with the same velocity and flow rate but at 24°C. The pressure drop across the heat pipe is 150 Pa. The supply air density is 1.35 kg/m3. The efficiency of the electric motor and the connected fan are 90 and 75%,respectively. Assuming the performance characteristics of the heat pipe are as shown in Figure 12, determine the sensible effectiveness, exit temperature of supply air to the space, energy recovered, and power supplied to the fan motor.Solution:From Figure 12, at face velocity of 2.5 m/s and with six rows, the effectiveness is about 58%. Because the mass flow rate of the air streams is the same and assuming their specific heat of 1 kJ/(kg·K) isthe same, then the exit temperature of the supply air to the space can be obtained from Equation (3a):
t2 = 10 - 0.58 {(5 kg/s)[1 kJ/(kg·K) / (5 kg/s)[1 kJ/(kg·K)] – (10 – 24)=18.12°C
The sensible energy recovered can be obtained from Equation (3c) as
qs=(5 kg/s)[1 kJ/(kg·K)](18.12 – 10)=40.6 kW
The supply air fan power can be obtained from Equation (11) as
Ps = 5 kg/s / 1.35 kg/m3(150 Pa) ⁄ [(0.9)(0.75)]=823 W or 0.823 kW
