DEC: Drying and Cooling Without Refrigeration

The cli­mate in a room is de­ter­mined by both the air tem­per­a­ture and rel­a­tive hu­mid­ity. In sum­mer the air en­ter­ing from out­side must usu­ally be cooled. Using con­ven­tional air-con­di­tion­ers, this process be­comes ex­pen­sive owing to the high en­ergy re­quired.

One al­ter­na­tive is DEC, which stands for ‘dessica­tive evap­o­ra­tive cool­ing’. This process dras­ti­cally re­duces the cost of room cli­mate con­trol and often al­lows air-con­di­tion­ers to be dis­pensed with al­to­gether.

In sum­mer DEC en­ables low-en­ergy de­hu­mid­i­fi­ca­tion and air cool­ing; in win­ter, the built-in sorp­tion rotor pro­vides ad­di­tional heat re­cov­ery to­gether with hu­mid­ity trans­fer.

DEC makes use of sev­eral phys­i­cal PWT­nom­ena, in­clud­ing cool­ing by evap­o­ra­tion (adi­a­batic cool­ing) and air dry­ing by sorp­tion. Air from out­side is dried by the sorp­tion rotor, then pre-cooled using a con­den­sa­tion rotor and fi­nally brought to the de­sired room tem­per­a­ture and hu­mid­ity via evap­o­ra­tive cool­ing.

DEC sys­tems are well suited to build­ings with large room vol­umes, such as au­di­to­ri­ums, of­fices and gov­ern­ment of­fices, ho­tels and print­ing works.

Example of a DEC System

This di­a­gram shows the DEC prin­ci­ple for sum­mer op­er­a­tion (out­side air ap­prox. 30°C, rel­a­tive hu­mid­ity ap­prox. 35%).

1–2 The sorp­tion rotor ex­tracts most of the mois­ture from the in­com­ing air. Just as air is cooled when steam is in­tro­duced, the re­verse oc­curs when it is dried - it be­comes warmer as ad­sorp­tion heat is re­leased. The air leaves the rotor con­sid­er­ably warmer and with much lower rel­a­tive hu­mid­ity.

2–3
The air now passes into a ro­tary heat ex­changer. Here the rotor cools the air using the stored cool­ness from the ex­haust airstream.

3–4
The air is fur­ther cooled in the hu­mid­i­fier via evap­o­ra­tive hu­mid­i­fi­ca­tion. The air en­ter­ing the build­ing is now at roughly 21°C with about 60% rel­a­tive hu­mid­ity and is thus within the ‘com­fort zone’.

4–5 In­side the build­ing the air be­comes warmer and the hu­mid­ity falls slightly.

5–6 Within the ex­haust airstream the used air tra­verses an­other hu­mid­i­fier and is again sig­nif­i­cantly cooled by evap­o­ra­tive cool­ing. Now it is sat­u­rated with mois­ture.

6–7 The ex­haust air is strongly heated in the ro­tary heat ex­changer by the heat stored from the sup­ply air; at the same time, the hu­mid­ity level falls con­sid­er­ably.

7–8 The air is fur­ther heated by an ex­ter­nal heat source (e.g. a solar ther­mal sys­tem, re­gen­er­a­tion air heater or, in sum­mer, un­used dis­trict heat­ing).

8–9 The high heat level binds the mois­ture into the air and the sorp­tion rotor is re­gen­er­ated by des­orp­tion.

Klin­gen­burg sup­plies all rel­e­vant com­po­nents for DEC sys­tems. Talk to us. we will be pleased to help you de­sign your in­di­vid­ual DEC so­lu­tion.

The Mol­lier h-x di­a­gram demon­strates the changes in terms of tem­per­a­ture, mois­ture and en­ergy con­tent of the air at the var­i­ous stages in our ex­am­ple.