Use code like this in your .jrxml file
<!-- Hides the Header Subreport when exporting to CSV -->
<property name="net.sf.jasperreports.export.csv.exclude.origin.band.1" value="pageHeader"/>
<property name="net.sf.jasperreports.export.csv.exclude.origin.report.1" value="HeaderPortrait"/>
<!-- Hides all fields in pageHeader except subreports when exporting to CSV -->
<property name="net.sf.jasperreports.export.csv.exclude.origin.band.2" value="pageHeader"/>
<!-- Hides the Footer Subreport when exporting to CSV -->
<property name="net.sf.jasperreports.export.csv.exclude.origin.band.3" value="pageFooter"/>
<property name="net.sf.jasperreports.export.csv.exclude.origin.report.3" value="FooterPortrait"/>
<!-- Hides the saerbi017sub001 Subreport when exporting to CSV -->
<property name="net.sf.jasperreports.export.csv.exclude.origin.band.4" value="pageHeader"/>
<property name="net.sf.jasperreports.export.csv.exclude.origin.band.4" value="noData"/>
<property name="net.sf.jasperreports.export.csv.exclude.origin.report.4" value="saerbi017sub001"/>
<!-- Stops fields in columnHeader to display more than once when exporting to CSV -->
<property name="net.sf.jasperreports.export.csv.exclude.origin.keep.first.band.5" value="columnHeader"/>
<!-- Hides the Summary Subreport when exporting to CSV -->
<property name="net.sf.jasperreports.export.csv.exclude.origin.band.6" value="summary"/>
<property name="net.sf.jasperreports.export.csv.exclude.origin.report.6" value="Summary"/>