PICCV or Circuit Setters

[jordi29]

Hello all,

I have a colleague (old school) at work who insists on the use of PICCV for a computer room air conditioner as basis of design. The Lieberts (our preferred vendor) come with either 2- or 3-way valves internal. We prefer 2-way for our datacenter. Either way, my partner insists in taking out the valve that comes with the Lieberts, only to replace them with externally controlled PICCV (Belimo). GPM is about 100 per Liebert. He claims, if we don't do this we would need a circuit setter per Air Handler.... The algorithms for controls (for valve modulation) that Liebert has have worked perfectly in other datacenters I've worked in.

I don't get it... am I missing something obvious?
Thanks!

 

[gerhardl]

You are probably not missing anything, but you are probably both correct.

An externally controlled 2/2 way valve will work 'straightforward' based on the input parameters, which could be taken directly from measure points within the actual application room/area, and thus directly act on factual readings at site. The homepage on the one mentioned shows a valvetype with good capacity for a given diameter(high Cv) and probably a similar wide regulating range.

I am not an expert on air conditioning systems as described, but a 3-way valve and/or internal programming could be a step removed from the actual readings. Eg.: the output could, under certain circumstances, probably be influenced by internal flow parameters (Cv), air capacity, heating/cooling capacity, internal valve carachteristics, influence from other sources or internal programming etc., and give output results contrary to expectations.

In most cases the standard package solution might probably run well. You should however be 100% sure this will be OK under all circumstances.

Generally there are common examples on such simple things as standard industrial heat exchangers where too complicated controls and three-way mixing has given great problems.

 

[btrueblood]

Pressure-independent control valves work on systems that have variable flow conditions, e.g. variable loads in chilled water HVAC piping, and especially time-variable loads in multi-branch piping system. You'd think a data center would have fairly constant loads, but I can imagine servers with various power saving schemes (sleep modes for drives, cpu's) that could have heat output varying over time. Probably not as strongly as in more heavily human-occupied spaces, but there should be some variation just with daily weather variations creating heat loads on the building walls.

Agree with gerhardl, 3-way mixing valves are a really dumb idea - you throw away a lot of energy when the 3-way valves dumps and mixes out chilled water.

I'd look for a valve that has the capacity you need, not picking one from the top of its rated flow range with no capacity above that rating. There are other, better pressure independent valves out there - google is your friend.