Heat transfer sheet assembly with an intermediate spacing feature

A heat transfer sheet assembly for a rotary regenerative heat exchanger, comprising:

• a first sheet element having a first profile comprising a plurality of parallel and elongate first and second sheet spacing features extending longitudinally in a gaseous flow direction, with a first repeat of said first profile being defined by and including the first and second sheet spacing features and a portion of the first sheet element extending between the first and second sheet spacing features;
• and
• a second sheet element of a length equivalent to the first sheet element, the second sheet element having a second profile comprising a complementary plurality of parallel and elongate third and fourth sheet spacing features with a second repeat of said second profile being defined by and including the third and fourth sheet spacing features and a portion of the second sheet element extending between the third and fourth sheet spacing features,
• the first sheet element being packed against the second sheet element with said first and third sheet spacing features seating against one another and the second and fourth sheet spacing features seating against one another, wherein the seated first and third sheet spacing features and the second and fourth sheet spacing features define a generally close sided elongate channel for gaseous flow therethrough,
• the first sheet element having lobular heat transfer undulations extending laterally and uninterrupted in between each of the first and second spacing features,
• the second sheet element further comprising an elongate fifth sheet spacing feature extending longitudinally along at least half a length of the second sheet element, intermediate each of the third and fourth sheet spacing features, the fifth sheet spacing feature comprising a lobe contacting at least some of the lobular heat transfer undulations between the first and second sheet spacing features of the first sheet element, the lobe of the fifth sheet spacing feature having an amplitude less than or equal to a spacing provided by the seated first and third sheet spacing features and the seated second and fourth sheet spacing features.