|
VRV/VRF versus Chilled water system
|
|
Source：Internet Author：Unknow Pubdate：2010-04-16
|
|
sridhar1312 (Mechanical)
11 Nov 09 7:05
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 (Mechanical)
11 Nov 09 13:51
字串6
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 字串9
Good luck knowledge is power
CptHk (Mechanical)
11 Nov 09 15:37
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 (Mechanical)
11 Nov 09 15:59
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) 字串2
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 (Mechanical)
12 Nov 09 4:55
daikin will sell you a 410 detector / alarm if you get into a pinch, but it isnt exactly cheap.
sridhar1312 (Mechanical)
12 Nov 09 21:19
has any one has technical comparison for VRF/VRV versus Chilled water system
字串6
SAK9 (Mechanical)
12 Nov 09 21:33
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 (Mechanical)
13 Nov 09 10:18
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. 字串3
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? 字串8
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 (Mechanical)
13 Nov 09 16:53
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 (Mechanical)
13 Nov 09 21:13
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.... 字串7
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 (Mechanical)
15 Nov 09 17:52
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 (Mechanical)
16 Nov 09 4:13
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. 字串8
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 (Mechanical)
16 Nov 09 13:54
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
字串8
ChrisConley (Mechanical)
16 Nov 09 14:22
Quote: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 (Mechanical)
16 Nov 09 15:25
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.
字串6
sridhar1312 (Mechanical)
22 Nov 09 23:29
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 (Mechanical)
23 Nov 09 9:52
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. 字串5
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.
字串6
coldmaster (Mechanical)
24 Nov 09 18:49
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 (Mechanical)
25 Nov 09 10:17
Coldmaster is correct, the lowest I found was 23 F. knowledge is power
mauricestoker (Mechanical)
25 Nov 09 11:16
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).
字串2
HerrKaLeun (Mechanical)
20 Jan 10 21:57
We recently installed a Mitsubishi VRF in Madison/WI. You need a backup system below freezing. Daikin/Mitsubishi rate it to -4°F... but don't recommend that. Several issues with compressor wear, low COP and freezing of coils. with a supplemental heating system you are golden.
Economics: their strength is when you have cooling/heating at the same time since it reuses that heat well. If you have mostly cooling only, or heating only... a chiller may be better. You really have to run a Trane TRACE simulation to evaluate economics. As a rule of thumb havingmany core zones, possible a server room will make a VRF economical when you need heating too.
Write and enforce really tight refrigerant leakage specifications. Refrigerant leaks are the Achilles heel. Obvioulsy a chiller is beter in that respect.
RossABQ (Mechanical)
22 Jan 10 9:29
字串4
I was under the impression that VRV/VRF systems are getting a boost because of LEED points? While LCC analysis may be the proper engineering evaluation, precious points for Eac1 (LEED 2.2) are a different story. How do they look on a whole-system basis for purely energy costs?
HerrKaLeun (Mechanical)
22 Jan 10 19:38
depends on case by case. You need to do an energy simulation. rule of thumb as mentioned above, have zones with likely heating and cooling at the same time. Like large core areas that need cooling when the perimeter needs heating, or server rooms. also avoids that whole reheat issue with badly designed VAV systems.
but rules of thumb don't get you LEED points
I think LEED 3.0 requires energy simulations. However, only two can simulate VRF systems. Trane TRACE is really good and also a design tool. EnergyPro is based on the DoE 2.1 engine from the stone ages. that really is not a good tool. You migth as well use the (free) eQuest. A Daikin salesman once recommended EnergyPro. then I bought TRACE because of all the chiller, boiler, ventialtion details it can calcualte. He then told me I made a mistake. Soem months later I met him again and he told me they (not sure if just his office, Or DAIKIN) tested it and found it not suitable for VRF. This tells me much about salesman recommendations and EnergyPRo. DoE does not have the VRF capability and will never have since it is not that detailed. 字串8
I'm digressing.. but you should consider a good software. Like with all HVAC, there is no perfect system that fits all.
marcoh (Mechanical)
2 Feb 10 7:33
I've installed quite a few VRF systems and many more chilled water systems and you need to consider each application on it merits.
- VRF is cheaper.
- VRF is more energy efficient than air cooled chiller plant.
- VRF is less efficient than water cooled chiller plant.
- VRF is 'plug and play' and simple to install
- VRF controls are simple and don't need to be programmed as per BMS systems.
- VRF FCU are limited to standard selection. Will required outside air preconditioning for high humidity/high outside air quantities.
- Check warranties if using VRF for 24/7 computer rooms. Daikin warranty is void if used for computer rooms!
- VRF systems are limited to the whomever supplied the original system. What happens if you need to replace a FCU in 10 years time? Not an issue with chilled water. 字串9
- VRF systems probably won't last as long as chilled water systems.
Generally I would say if an air cooled chiller is proposed, then a VRF system is probably a suitable alternative, especially for office applications (and using outside air preconditioning.
Waramanga (Mechanical)
10 Feb 10 6:03
My experience with the vrv systems is positive with two major drawbacks. Much shorter lifespan than chilled/hot water (high churn buildings only) and the temperature control at low load conditions is poor. Proper heat load calcs are a necessity (no over-sizing), condition OA before the FCU and even then expect some complaints in the in-between seasons.
dbarry14 (Mechanical)
23 Feb 10 23:53
I have designed several VRF systems, typically I use Sanyo or Mitsubishi. Everyone needs to remember there are heat pump (heating or cooling) and heat recovery (heating, cooling, or simultaneous) VRF systems. Also each mfg does things differenty. Sanyo will cool down to 14F. It will provide cooling lower if in simultaneous heating/cooling mode. The energy savings are enormous on VRF systems compared to chilled water, running one inverter driven compressor vs. a chiller and chilled water pumps. You also save a lot of space w/a VRF system. Plus VRF systems are QUIET! A VRF compressor vs. a chiller isn't even a comparison. It's like a whisper compared to a football game. Outside air does need to be treated independently of the VRF system. ERVs help reduce load additionally (if you can use them). VRF isn't the end all be all, but they do have their place if they are applied properly.
字串5
mauricestoker (Mechanical)
24 Feb 10 8:30
Ended up deciding on a mix.
VRF where space is available in condenser room, rooftop chillers for separate short stack runs occur.
Now just have to have asbestos surveys.
dalet57 (Industrial)
11 Mar 10 17:33
I am inquiring about a VRF system, we have been told about it's efficencies by our HVAC company. Anyone with any sucess with these types of units. 50 unit apartment building in a midwestern climate.
AnotherEllis (Mechanical)
3 Apr 10 23:14
I have several of my VRV and VRF designs installed and up and running here in my hot/humid climate. I've had nothing but good experiences so far. As far as VRF vs. Chilled Water, the individual project merits will determine the appropriate solution. 字串2
I have one 400 ton install that was originally designed as a small chilled water plant, but during schematic design the VRF beat it out on first cost. That install was an anomaly, and in other designs in this tonnage range the chilled water killed the VRF in LCC.
As for efficiency, yes a well designed chiller plant will generally beat out a VRF system, but the chilled water app falls on its face under 100 tons. The VRF does great in this range.
Also, I have a LEED v.2 for Schools project right now that I managed to hit 8 points on EA Credit 1 using DOAS with energy recovery wheels and Daikin VRV with oversized condensing units. This was about 60 tons total (small private school). Try that with chilled water at that tonnage!
ChrisConley (Mechanical)
5 Apr 10 16:21
What did you use to model the VRV system for LEED?
AnotherEllis (Mechanical)
5 Apr 10 23:35
字串8
On this one, EnergyGauge.
And I need to make a correction: I got 6 points on that project, not 8. Using a similar design on a renovation I anticipate 8 as per the model, but it has not yet been audited and accepted by the reviewers. Both projects had savings vs. the baseline model within 1% of each other, but the renovation scale gives more points.
On the renovation we are using Carrier's H.A.P. Both projects are v.2; they kicked off some time back then went on hiatus, but we registered both under the old rating system as the fundamental designs were set up to take advantage of the older point structure.
（Click：）
|
| Previous：effect of lowering chilled water supply Next：Estimating air changes per hour |
|
[ Add TO Favorites]
[TOP] [PRINT]
[CLOCE WINDOWS] |
|
|
|
