ASHRAE Journal - August 2009 - 78

Energy-Efficient Dehumidification By John Dieckmann, Member ASHRAE; Kurtis McKenney, and James Brodrick, Ph.D., Member ASHRAE Vapor Compression, Cromer Cycle ehumidification load with partial sensible load occurs with an estimated one-third of the primary energy consumption for air conditioning in the Southern region of the U.S., a quarter of the primary cooling energy in the Northeast region, and a quarter of the primary cooling energy in the Midwest region. The Southern region accounts for more than 60% of the total U.S. cooling energy consumption, while the Northeast and the Midwest regions account for approximately 10% and 12%, respectively. Therefore, choosing the right dehumidification approach is critical to saving energy. Dehumidification Basics Air ����i�i���r� ���� i����r �ir ����� �ib�� ����i�g) ��� ��humi�ify �h� �ir ������� ����i�g). C��v���i���� u�i��ry �ir ����i�i���r� �ypi����y h�v� ��humi� �ifi���i�� �������) ��p��i�y i� �h� r��g� �f 20% – 30% �f �h� ����� ����i�g ��� p��i�y, �r � ����ib�� h��� r��i� �SHR) �f 70% – 80%. A� � r��g� �f �mbi��� ����i�i���, �ypifi�� by high w���bu�b ��mp�r��ur� �r high r����iv� humi�i�y wi�h m���r��� ��mp�r��ur�, �h� ������ ����i�g ���� wi�� b� gr����r �h�� 30% �f �h� ����� ����i�g ����. Thi� �f��� ����� �� i����qu��� ��humi�ifi���i��, r�quiri�g �v�r����i�g �f �h� ����i�i���� �p��� �r u�� �f h�� g�� r�h���, b��h i��ffi�i��� pr���i���, �r ��mpr�mi��� i����r humi�i�y ����r�� ��� i����r �ir qu��i�y. Fur�h�rm�r�, �� bui��i�g ��v���p�� �r� impr�v��, �h� m�i� b���fi� i� r�� �u��� ����ib�� ����, wi�h ������ ����� 78 ASHRAE Journal b���mi�g � ��rg�r pr�p�r�i�� �f �h� ����� ����i�g ����. Wi�h�u� ����i�g �quipm��� �h�� ��� �ffi�i����y m��� ������ ���� i���p�������y �f ����ib�� �����, mu�h �f �h� p�����i�� ���rgy ��vi�g� fr�m impr�v�� bui��i�g ��v�� ��p�� wi�� ��� b� ��hi�v�� i� pr���i��. Thi� i��u� i� �i��� i� �h� DOE Bui��i�g T��h����gy R���m�p1, wh�r� i��m J i�, “Supp��m����� ��humi�if i���i�� �y���m� f�r humi� ��im����—D�v�� ��pm��� �f �ffi�i���, r��i�b��, ��w ���� �upp��m����� ��humi�ifi���i�� �y���m� f�r h��, humi� ��im���� �h�� �r� ��p�b�� �f m�i���i�i�g i���r��� RH b���w 50% �uri�g p�ri��� wh�� �h� ��m��� f�r ����ib�� ����i�g i� ��w.” Dehumidification Approaches I� � b��i� v�p�r ��mpr���i�� �y��� �ir ����i�i���r, m�i��ur� i� r�m�v�� by ����i�g �h� �ir �� b� ��humi�ifi�� b���w i�� ��w p�i��, ��u�i�g m�i��ur� �� ���� ashrae.org ����� �u� �f �h� �ir, �Figure 1a). Th� �ir i� ������ by � r�frig�r���� ����i�g ��i� ��h� �v�p�r���r) ��� m�i��ur� ��������� �� �h� fi� �urf��� �f �h� ��i� ��� �r�i�� �ff �h� ��i� by gr�vi�y i��� � ���������� p�� ��� i� ���� �� � �r�i�. Th� �m�u�� �f ��humi�ifi���i�� �h�� i� ����mp�i�h�� r����iv� �� �h� ����ib�� ����i�g i� i�h�r� ����y �imi��� by �h� f��� �h�� i� i� ������ ��ry �� r��u�� �h� ��mp�r��ur� �f �h� �ir �� r���h �h� p�i�� wh�r� m�i��ur� wi�� ��������. Figure 1b i��u��r���� �h� �imp���� ��� h����� ��humi�ifi���i�� �ppr���h, h�� g�� r�h���. Wi�h h�� g�� r�h���, �x���� ����ib�� ����i�g i� �imp�y u����� wi�h � h���i�g ��i� ��w���r��m �f �h� �v�p�r�� ��r. Wh�� high�pr���ur� v�p�r fr�m �h� ��mpr����r �i��h�rg� i� �h� ��ur�� �f h��� f�r r�h���i�g ��h� “h�� g��”), �x�r� ���rgy i� ��� u���, bu� �ig�ifi���� ���rgy i� �xp����� �� ����mp�i�h �h� ����ib�� ����i�g �h�� i� u�����. Thi� i� � high�y i��ffi�i��� w�y �� �b��i� ��humi�ifi��� �i�� wi�h r��u��� �r �� ����ib�� ����i�g. M�r��v�r, h�� g�� r�h��� r��u��� i� �i���� �r �� i��r���� i� �h� ��humi�ifi���i�� ��p��i�y �f �h� �ir ����i�i���r. Th� p�rf�rm���� �b��h �h� �ffi�i���y ��� �h� �m�u�� �f m�i��ur� r�m�v�� f�r � giv�� r�frig�r��� ��mpr����r ��p��i�y) ��� b� impr�v�� by u�i�g �h� ���� �ir ���vi�g �h� �v�p�r���r �� pr����� �h� ��� ��ri�g �ir b�f�r� i� ����r� �h� �v�p�r���r. Thi� i� ���� by r��up�r��i�g, ����wi�g �h� �v�p�r���r ��� ��mpr����r �� ���� �h� �ir �� � ��w�r ��mp�r��ur� ��� r�m�v� m�r� m�i��ur�, �� �h�w� i� Figure 1c. Wi�h r��up�r��iv� pr�����i�g ��� r�� h���i�g, �h� �v�r��� �ff��� i� �� �x�h��g� ����ib�� ����i�g ��p��i�y f�r ���i�i���� ������ ����i�g ��p��i�y. I� �h� Figure 1c ���figur��i��, � ��i� up��r��m ��� � ��i� ��w���r��m �f �h� �v�p�r���r p�rf�rm �h� r��up�r��iv� pr�����i�g ��� r�h���i�g. Th� h��� �h�� i� r�m�v�� fr�m �h� i���mi�g �ir i� �r���p�r��� by h��� pip�� �� �h� ��w���r��m ��i�, wh�r� i� i� �r���f�rr�� �� �h� ���� �ry �ir ���vi�g �h� �v�p�r���r. Thi� �rr��g�m���, whi�h i� pr��u��� ��mm�r�i���y, ��� ���r�y ��ub�� �h� ��humi�ifi���i�� ��p��i�y ��� r��u�� �h� ����ib�� ��p��i�y �r��u�i�g August 2009
ASHRAE Journal - August 2009

Table of Contents for the Digital Edition of ASHRAE Journal - August 2009
