VRV/VRF versus Chilled water system 5

[sridhar1312]

Off late I have come across manufacturer after manufacturer coming out with VRV /VRF system and aggressively .It is being marketed for most of the applications.I have found the economics does not work out in favor of the VRV /VRF compared to Chilled water system.

Even in VRV/VRF digital scroll as well as VFD driven compressors are in competition. At least in the INDIAN context where predominantly only cooling is required chilled water systems are economical and reliable.
Can any one throw light and let me know the strengths and limitations of VRV/VRF system especially where only cooling is needed.
Further when we use the VRF/VRV most of the indoor units are standard product having 2 row cooling coils and does not dehumidify to the extent is neeeded for coastal climate like Madras /Bombay

 

[cdxx139]

The big limitation I found was that the literature states the refrigerant lines can be as long as 500 feet, but when you read the fine print, after the first T from the condensing unit, you are limited to 135 feet to the furthest unit.

Also the condensing unit does nto have low ambient control, it trips at 23 degF ambient. (which may not be a problem in India, but is in Northeast USA).

As for ventilation, we had AHU's providing ventilation, and the VRV units were conditioning the spaces loads (it was a high computer load space).

We didnt use chilled water because it was a renovation space, and was confined by the 10" ceilings, and a Mitsubishi unit was able to accomodate.

I did not do a payback review.

I too used it for cooling only, but I do recall a heat recovery mode that is available. It works somehat like a condenser water loop, but you need a somewhat balanced system, so when half is heating in the winter about half need to be cooling

Good luck

knowledge is power

 

[CptHk]

I'd agree with cdxx139. Except 10" ceiling reminds me of the Stonehenge scene in Spinal Tap.

Also keep in mind ASHRAE 15, the mfr. reps did not initially remind me about that. It turns out that if you have a lot of small confined spaces served by one big VRF condensor, you either need to transfer to larger spaces or provide refrigerant detection alarms. Any point of leakage could release the whole system refrigerant volume into that one space with the leak. A Daikin employee at a local ASHRAE chapter meeting offered that tidbit during his presentation.

 

[cdxx139]

The 10" ceiling was from an existing supply plenum. They has diffisers in the grid of the ACT ceiling. (first time I saw this done on the supply side)

And the head of facilities had some reservations about the whole system. He didnt like the fact it was R-410 (becasue it uses higher pressures than R-22). I told him all the greener refrigerants are higher pressure, but he didnt care.

We looked at putting isolation valves in the refrigerant system, but upon further review, we decided against it. One reason was the connection of the valves would add additional possible points of leaking. So we kept them out.

Make sure to do the pressure test st 600 psig, and hold for 24 hours.

knowledge is power

 

[Waramanga]

daikin will sell you a 410 detector / alarm if you get into a pinch, but it isnt exactly cheap.

 

[sridhar1312]

has any one has technical comparison for VRF/VRV versus Chilled water system

 

[SAK9]

One thing against VRV is the refrigerant leak issue especiaaly if the system serves small rooms where it can cause oxygen depletion.So you need to limit the system size within reasonable limits based on smallest room area served.For eg if the room area is 10 sqm you would need to limit the refrigerant qty under less than 15 kg.There is a calculation provided in the Diakin manuals for this.The other issue will be the large number of units to be maintained and therefore lesser reliability than a chilled water system.
Dehumidification issues can be dealt with by having a dedicated unit to treat the fresh air

 

[GMcD]

The thing you have to remember about these VRF systems is that they are complete, proprietary systems, from the controls right up to the condensing units, refrigerant controllers, and all the system components other than the refrigerant piping and the dedicated outdoor air supply unit(s). That means you can't use "anybodys" building control and automation system to run these systems, you'll need a BacNet or Lonworks black box to connect from your building DDC system to the VRF system, and you can only monitor what it's doing, you can't control it.

Then, for any maintenance on these systems you need a guy with a refrigeration ticket, and you also need to watch local Codes for quantity of refrigerant in the system, leak detection, and ventilation requirements. You also have to deal with the original supplier/manufacturer - if it's a Mitsubishi system, you are locked-in for all the system components and accessories. You can't use Daikon stuff in a Mitsubishi system. One may also need a higher class of building engineer/facilities operator (Class 4 engineering ticket or better) to deal with these if it's a large system due to the higher quantity of pressurized refrigerant. As others have mentioned, there are strict limitations on the pipe lengths from the condensing unit to the furthest fan-coil.

In my opinion, a well designed water source heat pump system using the small ceiling mounted water-to-air heat pumps would be very close in energy performance, but gives one a much wider range of flexibility for systems components, controls, maintenance, and operation. Besides, you get a leak with a water source heat pump system, you have water at maybe 50 psig leaking. The VRF systems typically operate in the 300-400 psig range...fine, if it's a transient occupancy like a grocery store, but do you really want to have 300+psig refrigerant piping running above office workers who are there 10 hours a day?

I think the VRF systems may have a place for retro-fits to older buildings, but as long as the designer and Client understand the limitations and maintenance issues, it is a reasonable option. Me, I'm still going to recommend 4-pipe fan-coil or water source heat pumps before VRF systems.

 

[ChrisConley]

I'm considering my first VRV (VRF) system on a new construction. My general preference is radiant heat/radiant cooling or 4 pipe fan coil but the system is being proposed as a near equivalent on energy performance, but with a significant reduction on capital cost. I'm still putting numbers together, but I'd love to hear anyone else's experience in first-cost comparisons.

 

[GMcD]

Chris: ask yourself why the low first cost is being offered - maybe there is some nice coin to be had for the maintenance contract, considering that you are going to be locked-in to the successful supplier for all the on-going parts and maintenance....

Make sure the capital cost for the VRF system includes everything, including pipe insulation and the DOAS (Dedicated Outdoor Air System) controls to be fairly costed against your radiant and/or 4-pipe fan-coil.

 

[Waramanga]

Our analysis of the VRF vs chilled water has shown that the VRF is definitely not the better option when it comes to total lifetime costs, but if you only need 15 as opposed to 30+ years....

 

[sridhar1312]

Thank you yes where ever Clients had requested we have done analysis we find the Life Cycle cost of Chilled water system is economical compared to VRV systems.
As with the chilled water system the Chiller required shall be as low as 60%to 80 % of the Peak load as long as the Low side equipments are designed for the Peak Load.The above flexibility is not available in any other system including VRV.
Apart from the above in this part the qualified technical skilled person are scarce and for VRV site work is critical as we have found failure rate are very high.
None of the manufacturer or contractor do not suggest the refrigerant leak detection alarm nor even raise about it.

Another key issue is Pressure testing upto 600 PSI is rarley done by any contractor.

 

[cdxx139]

You put it all contractor requirements in the specification.

I used the Mitsubishi system, and did some training. The contractor had to be "certified", meaning they went to training. And the manufacturer provided a commisioing list, and one of the steps was pressure testing. This was also a requirement of a project. I was lucky to have a contractor thaty cared about the project, and left the pressure testing over the weekend.

If you own it in the spec, they are responsible. Whether they actually do it, depends on how much you check up on them

knowledge is power

 

[ChrisConley]

ask yourself why the low first cost is being offered

My understanding of the reduced first costs comes primarily from the installation (5/8" copper pipe compared to 4" chilled water mains). There's some reduced control complexity (no humidity reset required) that also play a factor.

 

[GMcD]

Geez Chris - "some reduced control complexity"?? Trying to control warm and cold refrigerant simultaneously while modulating a variable speed condensing unit refrigerant compressor is about as complicated as it gets. While on the surface, it looks like reduced control stuff might be apparent- what's happening in all those controller boxes, and the packaged controls that come with the VRF system?

You can't simply superficially compare a "4 inch" chilled water pipe to a 5/8" copper tube - look at the distribution mains sizes for the VRF, and compare fairly to a decent chilled water delta T with right-sizing the diversity of the CHW system piping. Even assembling 2.5 inch and 3 inch Schedule 20 or Schedule 40 chilled water piping can't be that much more than the cost and labour involved in high pressure all-brazed or sil-fossed refrigerant pipe.

 

[sridhar1312]

Yes the complicity involved in VRF/VRV are continuous and have to be dependent on the Vendor who has supplied for life of equipment.Whereas the chilled water system any reasonable good piping vendor can do it.
End product in chiller chilled water does not get affected by the chiller as it is factory made and tested, where as the VRF/VRV is connected at site where the quality of pipe used, quality of brazing, pressure testing evacuating can affect the VRF/VRV system.

Control system for chilled water can be attended by any control vendor unlike the VRF /VRV where each vendor has different protocol and many times even with the vendor only few guys are trained.

 

[mauricestoker]

I think it depends on application. For existing high rise construction, especially while occupied, the reduction in penetrations and fire proofing, often substantially lower asbestos impact, and elimination of large water filled lines around electrical and teledata equipment has substantial benefits. I've been looking at it for stacks of teledata closets going through seven floors, and chilled water is not an economic alternative (existing chilled water plant is about 200 TR short, and constant primary/constant secondary distribution). For unoccupied, vertical stacks in an occupied building with probable asbestos, I can't think of a better alternative, and have been talking to others that have installed Daikin (as well as the local rep). We have used smaller Daikin systems, they have worked very well, and the O&M shops are very happy after one year.

At the same time the customer wants to renovate 20 single story buildings, adjacent to two production wells out of service for eleven years of plume modeling. Initial scope was replacement in kind with DX units. I wouldn't even think of VRV for that application, it will be a GSHP, preferably with dedicated MOAU. You play with the cards you are dealt.

I wouldn't trust chilled water controls to just anyone, as what I am currently working on is the result of letting just anyone work on controls. If you have ever seen a 1-1/2" line supporting a 3" and 2" line (because the chilled water line was there, the assumption seems to have always been capacity exists) because the scope said to connect to existing chilled water distribution, you would know what I mean. If you are going to connect to existing chiller plant, you still need to verify capacity and distribution is present, that you don't have just any person sizing valves, and that you don't have secondary or tertiary controls defeating the system control. May sound ludicrous, but I am seeing that on a current job.

 

[coldmaster]

Careful applying the VRF to tele/data closets. These units don't have the same low ambient operation as their smaller (1 indoor :1 outdoor) cousins...VRF won't cool during cold winters.

 

[cdxx139]

Coldmaster is correct, the lowest I found was 23 F.

knowledge is power

 

[mauricestoker]

Glad you brought that up. I was planning main install in an abandoned condenser room (large amount of walk-ins)to cover three stacks of rooms going up seven floors and didn't address it for a couple short stacks (three floors). Those will be low ambient. Finding a routing around the asbestos, infectious disease control and interim life safety requirements rather limited any consideration of using chilled water (along with an existing shortage of capacity).