VRF / VRV Air Conditioning

Normally district cooling plant supply chilled water to villas and building. Your case also can do it that way.

v1406 quote "need to be mentioned here that the ambient temperature can reach upto 50 deg."

Maybe I missed something but If the temp only reaches 50 degrees why would you need an air conditioning system?

He is talking about degrees Celsius. Not everyone in the world is stuck with that quaint old fahrenheit system.

VAV (variable air volume) and VRF (variable refrigerant flow) systems will be awkward to meter for billing to the individual apartments; whereas individual through-wall units are easy to attach to the electrical metering per unit.

This places you into sort of a dilemma: easy individual metering vs a more efficient overall system. The question you pose is really good, but it might be hard to pin down the best approach.

I'm just thinking out loud about metering for the VAV and VRF systems. You say this is the in the gulf, and I guess that means the Arabian gulf, not the Gulf of Mexico, so requirements and expectations on metering accurately might not be quite as high / fussy as in the US.

I'm guessing that with a not unreasonable amount of effort, you can monitor some things like the flow rate of refrigerant, the time (to integrate that flow rate), and the temperature of the refrigerant to each "customer" (each of the 350 units, iiuc) (thinking of the VRF system), and maybe something similar for the VAV system.

Then use that integrated flow rate and temperature to calculate something like an estimated "heat" flow (cooling units--BTUs?) to each unit. Do this on a basis to match the electical billing. Then divide the total monthly operating cost by the total number of cooling units to get a unit cost, then multiply that unit cost by the number of cooling units a customer has used over the last month.

Sounds complicated, but something like a PLC could do this. (This assumes that flow of refrigerant is controlled to each customer anyway, and that it wouldn't bee too hard to get an estimate of flow to each customer--worst case, for a solenoid valve, just use the time the valve is open--for a modulated valve, worst case, use something like the valve position setpoint.

Or, just capture the settings of their thermostat and the ambient temperature in the unit.

I don't expect any of these means to give 100% accuracy. I'd make sure this is clear to the property owner / developer, and then included in the lease or sale agreement to each customer unit. Give them the option to pay to (have you) install much more accurate metering equipment if they want. Otherwise, they accept the results of the "metering" as described.

Not a straightforward solution, but if a VAV or VRF results in significant overall capital or operating savings, I'd hate to see the opportunity lost.

Hold it. Let's not get too fancy.

I've lived and worked there for 2.5 years. I've seen the 50'C and higher outdoor air temperature.

My strong suggestion is to keep it simple as on-going maintenance, operation and repair will be challenging.

In that part of the world, access to skilled trades people and access to funding for maintenace and repair is hard to get and harder to sustain.

Go with your traditional split systems with condensor units roof mounted (somewhat out-of-sight) or with strap-on wall units and use the electrical energy meter to do all the individual reporting that is needed.

Your benefits will be:

1. Metering for HVAC comes free because you will already have an electrical energy meter for other reasons.

2. You will find spare parts more easily for these types of A/C units.

3. Skills to service and repair or replace major components will be more available.

4. Multiple units will not require a trained group of operators to keep a central system going.

5. No water treatment chemistry to worry about compared to a central Chiller Water plant.

6. Any central system failure will affect multiple residences (perhaps all residences) compared to affecting a room or two in a single residence.

7. Friendly relations between facility operations and residents because comfort is delivered, complaints of being too hot are minimized, and cool heads will prevail.

I recall that when the 5 Ton A/C unit serving my house ground floor failed, it was a major event and everyone was close to panic stations as it was almost 50'C outdoors, and tempers were flying...

v1406,

Good topic, very apt for the present concerns on energy, environment et al. As Guest pointed out, one way is to go the District Cooling way - but then the size of the project is a deterent - too small!

VRF is the way to go and it is just right for the application you are working on, there are some pretty good products from Mitsubishi and McQuay which should fit your bill like a glove. It has all what you are looking for in terms of energy savings, initial investments, ease of operation and maintenance. You would do well to get in touch with either of the manufacturers for more details.

"The greater the obstacle, the more glory in overcoming it." -- David Hume (Scottish Philosopher)

From the best responders to your question it seems the concept of using a variable refrigerant flow machine(s) has merit.

It seems designs of variable refrigerant flow compressors are improving. My understanding is that scroll compressors can operate at turn-down ratios not achievable with other compressor designs.

It that is the case, maybe the question is how are you going to measure the refrigerant flow to each house, and also, how much refrigerant can you afford?

Do you have an "energy meter" in mind?

I have similar questions with respect to restaurant and small market refrigeration.

I don't like them for a number of resons. !. You have a failure you have multiple failures by design. I and my employees can work on these units but not very many others can so you would be held captive. The parts are not generic in most cases so you have to look to OEM, (price and availability), R-410 loses capacity at that ambient and your efficiency degrades startinh around 95'f (I'm American). With your average wet bulb in that area you would probably be smart to look at the cost and efficiency of chilled water, fan coils and water cooled chillers with Turbo Core compressors and R134a. If you take the total cost own over say 10 years I believe your answer is evident. Generic parts and the only replacement part on the compressors is the capacitor in most cases. The control protocol is modbus rtu which makes it very easy to integrate with most other control systems.

I forgot to mention that I don't believe you have much of a latent load to consider, it's all sensible so you can operate at a higher coil temperature which also adds to seer. Love projects like this because it's a totally new set of parameters. Hope you keep us posted. Love to see input from Tornado and Lynch on this, they add motivation to the design process.

hi

thanks for your comments. but still what remains to be answered is whether it is advisable to go for vrf sysetem in small houses with say 10 split ac requirements? in such cases the roof can easily accomodate the outdoor units.

is it going to be just a gimmick .......... a good technology but unsuitable for this application in small houses?? why i ask is coz in no way can we have shared metering for electrical consumption so must have individual vrf unit for EACH house..... thats where lies the doubt... will it still be beneficial in such applications??

thanks again.

If you are doing only one house per system it's great. I was under the impression you were intending to serve multiple houses on each system. McQuay is a nice product but the service and parts are terrible in the US. Mitsubishi is better to deal with but I have not seen a 10 zone system from them yet. For that many systems you should be able to get a free factory training class for the guys installing the piping, the placement is critical for the long term. In the US they won't sell to you unless you get the certification.

If you want to minimize the out door units than you will have to use a central chiller plant, that will supply chilled water for each unit on demand.

The other option is in the middle with the use of "ductless" multi zone units. LG, Mitsubishi, Sanyo, etc.

The other end is a single system per unit.

Pros for the first. One unit, one condenser or more than likely an evaporative cooling tower for the condenser. It can be designed for maximum efficiency. Cons; lose that system, and lose cooling for the entire complex. You will need a designed and engineered installation. Large investment and more complicated.

Pros for the other end. each unit has its own independent system. A good HVAC company can do it using of the shelf components. Lose one and just one unit is down. Cons; a whole lot of equipment to be maintained and where do you place 350 condensing units?

The middle is a mixture of the two.

It is up to the client to decide what is most important to them!

I have dealt with one to many clients that want HVAC systems that can not be seen, require little or no maintenance, are reliable, can be serviced by the local handy man, will not effect the entire building is a component fails as they are not willing to pay for secondary pumps etc., and it must be as CHEAP as possible!

There is no free lunch.

If the customer wants reliability, esthetic's, quality, etc. they will have to pay.

If they want to cheap out, than it might be best to run away, as the results will haunt you for ever.

Have your client set their priorities and start from that point. There is always a trade off on all concepts.

When first starting a construction project,many people get a utility pole that

comes with an electric meter and most of the time the bill is figured to cost

about 25.00 dollars.or maybe even less but the electric company connects

the whole house to the main wire after its inspected.If these small units you

are building are mostly about cost reduction savings . You could shop for small a/c

units that have just been invented,that are energy efficient and ask the

electric company if you can run it off of a utility Pole.ds

I lived in a housing area in the Gulf region that had central chilled-water plants for blocks of 30-40 homes. Due to adequate back-up compresssors & pumps it was very dependable & efficient. Also avoided maintenance headaches with individual powered units. It may be possible to just distribute the op cost among the occupied units.

That's the rub of this whole inquiry: how to charge occupants according to actual individual usage vs some kind pro rata average.

350 individual compressor/condenser/evaporator units are easy to meter electrically. The air-cooled condensing is not the most efficient, but the fact of only one heat transfer step from refrigerant to room air compensates somewhat for this.

A central system (chilled water of VRF) lends itself to evaporative condensing. This would be an advantage in dry climates, but with water available. It would be terrible in Dahran (design WB 86°F = 30°C).

Chilled water is easy enough to meter as far as volume goes, but its value depends also on its temperature. Thus a simple water meter might not be sufficient to meet the local laws on weights and measures for trade. In a similar fashion, as Rhkramer suggests, it is theoretically possible to measure refrigerant liquid flow along with relevant pressure/temperature. But I doubt that any commerce laws would know this, and renters might find the whole rationale hard to understand.

Unfortunately, it would take a book to survey all the options here, especially as to what local regulations may permit. (These few remarks do not equal a doctoral thesis. which could be desirable here.)

Hi Tornado - How's things in Alaska these days???? Ever been to Daharan? - I been there & done that!! . Lived there for 5+ yrs & rarely saw RH above 30% & that sure didn't reach wet bulb of 86F. It only rained once the Whole Time. Maybe in Ras Tanura right on the Gulf where it was sultry most time, but they had central evap units that seemed to work well.. The OP mentions consideration of maintenance, efficiency & a dozen more items & then questions about an analysis of (feasibility) of individualy metering each house......

Maybe there is a misprint in the WB data I've seen. I haven't been there for a personal check. 30% RH and 120°DB isn't far from 86°WB.

Well if it ever had got up to 120F I'd have come back sooner!!! Actually 103 to 108F ain't bad when the humidity is low, & that's only in the 2 hot months. Regards, Bob.............................................

On the metering side you could look at how hot water is done in high-rise residential systems. It's a fairly simple remote readable system.

As user temperature setting is a function of mass flow - flow used, aught to be an equatable basis for billing split.

As good a start point as any

Hey 34.5 I've lived in a complex of 33 units which featured a central hws. For me it didn't work due to the distance from the heaters, so we had a lag to get "hot" water - not warm.

In the case of cooling however, I can't see why a central chilled water system wouldn't work Surely a case of 'smart metering' - and they do exist.

True - it's a pay and wait for hot "unfairness" - especially if you use 'random little bits', rather than organising hot water usage into a 'top to tail' schedule of showers, laundry, washing up.

But this is actually a 'constant delivery' system - or the start up dwell 'cost' is maybe once per day - for the truly "don't know how a thermostat works" crowd.

Break down your plan into most-efficient pieces.

VRF indoor units can be ducted as well as ductless, so if you need to serve multiple rooms in one unit, it's 'possible' you could do each unit with one or two zones/terminals.

Efficiency in VRF systems comes from the diversity of loads, some spaces needing cooling while others do not, and combining these multiple terminal units to a common heatpump that can vary it's output efficiently. The "best" efficiency gains come when some spaces need cooling while others, at the same time, need heating, with a distributed 'black box' allowing the terminals to play off each other by directing the refrigerant/gas to each, with the central heat pump sitting idle or at low capacity and using little energy.

IF you do NOT have a situation with varied load profiles...then you do NOT have a situation that meets the 'best application' for VRF. Look at another system type. If you DO, then it is possible you will have a good match, so continue on.

How far away are the units physically, and can you run multiple refrigerant lines to one central heatpump from multiple tenant units? If so, then your next question is locating the unit and deciding what type.

The largest segment of these units is the air-source heatpump. You need air that is capable of taking the energy away (in cooling mode) or containing energy to take (in heating mode). If your dominant load is very dry, hot air that does not easily take heat energy off of an outside air coil, then you may not want to look at any air-source heatpump, whether it serves VRF distribution or standard split-systems. In that climate, you may well be better off with a water-source system.

Next: If you wish to look at watersource heatpumps for the inside loads, you can put a central WSHP unit in each home and duct to rooms, and decide then what your best heatsink/source may be. You can still use VRF as well, btw, since the outside VRF-Heatpump can be a watersource unit! This could be coupled to a community geothermal wellfield (very efficient, btw) or you can run a simple community waterloop to a central evaporator.

Either a ground-loop or an evaporator-cooled loop will avoid any kind of chiller plant altogether, just cool the loop and run water at ambient temperatures. The loop itself picks up much less ambient heat that way, is cheaper to run, no condensation or special maintenance like a chilled-water system, lower insulation requirements, etc.

My recommendation? If you go WSHP terminal equipment in each home, instead of VRF terminals, then they only tie onto a buried water loop. NO outside equipment at all for any home. No worries about the complexity of billing a portion of the VRF-heatpump or refrigerant metering for electricity usage. There is only the (buried) central community evaporator loop to pay for, which is central pumping, spray pumps, and fans, just estimate it, split it up, adjust it once a year if needed.