After modified the file \apps\redmine\conf\httpd-vhosts.conf：

<VirtualHost *:8080>
ServerName redmine.example.com
ServerAlias www.redmine.example.com
DocumentRoot "D:\App\Bitnami\redmine-3.3.0-0/apps/redmine/htdocs/public"
<Directory "D:\App\Bitnami\redmine-3.3.0-0/apps/redmine/htdocs/public">
Options -MultiViews
allow from all
</Directory>

Timeout 1200 # wuyan add

RewriteEngine On
RewriteRule ^/(.*)$ balancer://redminecluster%{REQUEST_URI} [P,QSA,L]
<Proxy balancer://redminecluster>
BalancerMember http://127.0.0.1:3001 timeout=1200 # wuyan modify
BalancerMember http://127.0.0.1:3002 timeout=1200 # wuyan modify
</Proxy>

Include "D:\App\Bitnami\redmine-3.3.0-0/apps/redmine/conf/httpd-app.conf"
</VirtualHost>

Now everything seems ok! 

redmine export long csv file failed: 502 proxy error