Chilled water treatment

I have a chilled water system supplying one ahu for building air con that is currently been working on water only. I've been asked to make this a glycol mix so that it's temp can be lowered. the pipework is a mix of plastic and copper, the chillers are York with plate heat ex's.
My questions are;
what glycol should I use?
to what concentration should I make it?
can I use a hydrometer to measure this as I don't know how much water there is and will not be draining?
if so where can I get a hydrometer from or is there another way of measuring the concentration?

I would appretiate answers to any of those questions or just pointing in the right direction for info.
Many thanks.
ben

Hi First check that York chiller/ compressor can handle lower evaporating conditions, then select either ethylene glycol [ the cheaper one ] or mono propylene the food grade option, but expensive. Either will not effect copper or plastic, but make sure you add anti-corrosion as well. generally glycols are mixed in volume ratios, for example 30% gives an approx freeze temp of -10'C, call a chemicals supply co and ask for specific mix ratios. When testing with hydrometer chill sample to approx operating temp and check specific density at that temp, other wise you get totally confused with readings. With the plastic pipe work check against manufacturers operating minimum temps as plastic get super brittle any where near 0'C, even ABS tha is rated to -40'C cracks if there is pipe movement [ learnt the hard way, replaced withs/s ] You cold ask some home brewers to borrow there hydrometer The chemical supplier with supply a chart with all readings at different mix ratios..As a rule of thumb I generally select a freeze temp 10'C below what you want to ciculate at.
hope this helps, regards Magoo