Sensible Heat Factor / capacity of Inverter split Systems at part load?

Hi guys & girls. Apologies for the length of this one but pls bare with me.<o></o>

So far no manufacturer has been able to give me any definitive answers or data on this so I thought I’d open it up to a wider audience for your opinions and theory’s. <o></o>
OK we all know that comfort cooling DX mini splits get installed in server rooms and the like (small to medium size rooms up to 30-35m2 or 30-40kW of cooling). <o></o>

We also know that mini splits are not the right equipment to use for this application – low sensible / high latent heat capacities for what is a high sensible application. However, like it or not, splits do get used for server rooms because:-<o></o>

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• ·Mini splits are available ex-stock (close control systems are normally built to order and 6 weeks is normally the minimum availability).<o></o>

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• ·They have a wide range of compact light weight indoor unit types that don’t take up valuable floor space, high wall units being the most popular (close control units are much larger / heavier & more difficult to locate in small rooms. Let’s face it some of the close control units are larger than a couple of server racks).<o></o>

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• They are cheaper to buy / install than close control systems.<o></o>

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• They are available up to 14kW capacity in 1ph power supplies and have low starting currents (some as low as 5amps). Most close control systems are 3ph above 5kW and have DOL start.<o></o>

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• They are capable of long pipe-runs (up to 70m on larger sizes) and need no special oil traps, double suction risers or oil separators as do some close control systems.<o></o>

As we know the big draw back with comfort cooling splits (when applied to server rooms) is their low sensible heat capacity which is 0.7 at best. This is fine for cooling people but not equipment and causes low room humidity, static issues and can lead to indoor unit freeze ups if the set point is set too low with a low indoor fan speed. The other area that gets overlooked is that cooling kW for cooling KW splits have a much lower air volume than close control units. Close control units need the higher air volume to achieve the high sensible cooling ratios and temperature sampling / air change rates that allows them to control to ±1°c of set point, which of course, most comfort cooling systems cannot do.<o></o>
So consider the following application:-<o></o>
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• Server room. <o></o>

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• Cooling Load , say 21kW sensible, 23.5kW Total (SHF of 0.9)<o></o>

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• Room design 22-23°c / 50%RH<o></o>

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• Design external ambient 30°c<o></o>

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• Proposed Equipment 4 off R410a High wall split systems capable of 10.6kW Total & 7.5kw sensible cooling each at the above conditions.<o></o>

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• Indoor fans on manual high speed only.<o></o>

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• Installed Sensible capacity 4 x 7.5kW = 30kW (N+1 if you will).<o></o>

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• Installed Latent capacity = 3.1kW per system x 4 = 12.4kW against required 2.5kW.<o></o>

The plan is to run all 4 split systems all the time i.e. no run & standby control strategy. So, in theory with all 4 systems running (30kW sensible cooling available against a 21kW max load) the Inverter controlled compressors will reduce their capacity proportionately to approximately 70% each on a design day and probably even lower at other times of the year.<o></o>

Question – what is the SHF of a 10.6kW (Total) Inverter split system when it’s running at 70% part load capacity? <o></o>

You can probably see where I’m going with this. If we installed extra Inverter split systems for additional capacity / redundancy reasons and then run them all together the SHF of each unit at a part load condition should be higher than the normal 0.7. In which case, they will not extract as much moisture as they do at full capacity. This partially over comes the low humidity complaint normally associated with mini splits in server rooms.<o></o>

Variable speed Inverter systems can control to quite close tolerances – close enough for small server rooms so this should not be an issue either. <o></o>

Has anyone ever seen part load SHF data published by any split system manufacturer or have you got any thoughts on this theoretical approach?<o></o>

Enjoy<o>:p></o>:p>

Take the easy route - fit a wall mounted humidiier. ;)

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Originally Posted by Brian_UK

Take the easy route - fit a wall mounted humidiier. ;)

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Thats toooo easy Brian.

But the wall mounted humidifier option will work.

The manufacturers dont provide that part load data because they dont wont to encourage contractor to mis apply the equipment.

Allthough you can expect the local sales rep to be quite happy to reccomend the high wall split as acceptable solution because he just needs the sale regardles of the application.

No manufacturer of standard comfort cooling splits will publish data for room condition of lower than 15 deg C WB.
The units are just not designed to cope below that condition.

but

enter any computer room being cooled with standard splits & measure the humidity

you will almost always find the humidity arround 30% RH & 11 or 12 deg C WB.

At this condition most standard splits with arround 0.7 SHF will be operating at coil frost prevention conditions & thats why iced up coils are often a problem in this application.

So in this case as the manufacturer does not publish any cooling performance data for on coil less than 15 deg C WB then the contractor must put thumb in air & make best guess.

Most opt to oversize units.

Some of the premium quality inverter systems constantly monitor the indoor coil temperature & slow down the compressor to prevent low coil temp & frost.
In this case the system runs permanantly at slow compressor speed to prevent coil frost & not to control room temp.

You pay for 10kw system but get about 5 or 6 kw cooling at best.

At least you dont get all the problems with the old fixed speed units stopping every 5 mins on coil frost prevention & smashing the compressor after 100,000 starts in 12 months 24/7 operation.

but

introduce some humidity with fresh air & or humidifier
then
with wet bulb temp higher than 15 deg C the systems will ramp right up & only slow down near set temp.

BTW
Can anyone provide a link to any manufactures web site which has cooling performance data for any mass produced standard comfort cooling split systems at below 15 deg C WB on coil condition ?

Hi Thermatech.

If the room is controlled to 22c & if the installed capacity is in excess of the load the splits would not be at full capacity. Therefore the ent wb temp would not be so low because the coil SHF would be higher than at full capacity.
In theory if each split system is running at 50% capacity the TD across each coil will be half of what it is at full capacity with the same air volume. A higher supply air temp means a higher evap temp an less moisture extracted.

I have seen data for an Lennox Inverter close control system at part load/speeds. The SHF is virtually 1 until it gets to 80-90% of its full speed / capacity at which point the SHF starts to drop to 0.95,0.9,0.85.
I'm not suggesting for one minute that the split will be able to achieve the same levels but the same principle must apply. Fixed indoor coil volume with reduced capacity outdoor capacity = higher SHF. It's same principle used by the likes of Marstair to get higher SHF's on their fixed speed split systems - Over sized indoor unit conected to smaller capacity outdoor unit.

There is however one snag with my theory. The extra capcity installed at day 1 to achieve all of the above will be dissappear in less than 6 months becase the IT techs will have stuffed another 15-20 blade servers in the racks which will eat all of the spare capacity up.

Long before ( many years) inverter split systems were available I was trouble shooting VRF systems installed in computer rooms. (The better inverter splits have similar control stratagy as VRF)

Consultants & contractors could not understand why VRF system performance was so poor in this aplication.

The plain & simple fact is
that
when there is no moisture being added into the heat load in the room the humidity will be reduced & reduced & reduced untill the WB is well below the minumum of 15 deg C WB.
Because if ever the humidity level creeps up above 15 deg C wb then the inverter ramps up the compressor & the indoor unit sucks more moisture out of the room & the WB drops again below 15.

The old mix match on Marstair high/low systems was a good solution to provide cost effective high SHR but even then they had compressor failures & cracked suction pipe at compressor due to the constant stop start operation of the comp.

I have found the best solution for split systems & VRF systems which have been mis applied into high sensible computer room applications is

1/ to get some moisture into the room
2/ ensure a good supply & return air flow between the computor cabinets & the indoor unit
3/ use additional head pressure control for higher discharge pressure which makes higher evaporating temp at the indoor unit which reduces dehumidification & helps reduce coil frost prevention

But its not ideal & never will be.

Thats why for instance Mitsubishi Electric make a dedicated high sensible cooling VRF system which can be used in this type of application.

But like most high SHR kit it costs more.

Hi there,
I believe that with a SANYO SPW system you can fit an oversized indoor unit to a smaller capacity outdoor unit and alter the setup programming parameters. This will give you a higher sensible capacity.

Worth giving Sanyo technical a call.

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Originally Posted by Electrocoolman

Hi there,
I believe that with a SANYO SPW system you can fit an oversized indoor unit to a smaller capacity outdoor unit and alter the setup programming parameters. This will give you a higher sensible capacity.

Worth giving Sanyo technical a call.

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That interesting Electro. Will contact Sanyo to discuss. Only snag is they don't do a nom 10kW high wall model as far as I know. In fact, there are very few manufacturers that do offer 10kW Inverter High wall models. ME, Daikin & Hitachi I know of but that's about it.
I believe on the Hitachi IVX systems you can set a power / capacity limit (for energy saving) at 75 or 50% via the remote control. Should have a similar effect.
Like you say a 10kW indoor unit with a smaller 7.1kW outdoor would be a better solution but no one seems to offer or want to sanction that combination. SHF would then be up around 0.9 which would be right on the money.
Some more research needed I think.

If the manufacturer can provide full warranty for this application
& allow the larger size indoor unit
& can provide information on correct refrigeration pipe size for the combination options
& provide data for the sensible cooling capacity at lower WB room temp with the mix match of indoor / outdoor size
then
you can select the correct size combination of units.
but
if they cannot provide data & warranty
then
you are on your own.

As has been said on this site before
the first major manufacturer to provide cost effective proper high sensible wall mount split system for computer room application should sell lots.

Quote:

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Originally Posted by Thermatech

If the manufacturer can provide full warranty for this application
& allow the larger size indoor unit
& can provide information on correct refrigeration pipe size for the combination options
& provide data for the sensible cooling capacity at lower WB room temp with the mix match of indoor / outdoor size
then
you can select the correct size combination of units.
but
if they cannot provide data & warranty
then
you are on your own.

As has been said on this site before
the first major manufacturer to provide cost effective proper high sensible wall mount split system for computer room application should sell lots.

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Thermatech. You sound like you might work for Mitsi Electric or another manufacturer? Please come clean an advise your position?
I am am a A/C contractor / installer & just seeking to to resolve an issue that I see every day. I totally agree there is a market out there for the system we are talking about. Problem is no one understands or believes in it!!!
Come back!!!!!!

No problem

I am an independant specialist
I have worked in the ac industry for 32 years
over the years I have worked for a number of major & minor manufactures
in a number of possitions from apprentice technician through to service manager

Now I am semi retired & just work part time
I provide specialist trouble shooting & commissioning assistance to a number of manufacturers, distributors & ac contractors

This issue of small computerroom high sensible cooling load application with standard comfort cooling split & VRF systems is a problem I have had to trouble shoot many many times

Over the years
I have experianced this situation form the perpective of
installation contractor
maintenance contractor
distributor
manufacturer

When any manufacturer can produce a reliable wall mounted split system with high sensible heat capacity of about 10kw then contractors would buy them by the container load.

Untill then most will continue to use standard comfort cooling split systems which are far from ideal for computer room application

Techguy..glad your back...any experience of SANYO SPW in this situation?

Thermatec, for this application you can use 4 x Daikin RZQ100 units which offer low humidity settings for this type of application, you can use a change over panel so that only 2 units run at any one time 2 for master and 2 for slave and change over on a weekly basis, this control system also has an external thermostat so that if the two units can not cope with the load and go into an alarm fault of say 25 degress, what ever you set it up for the second two units will kick in, this strategy will reduce the overall number of starts on all of the units, protecting the compressors.
I would also suggest a humidifyer as to keep the room at 50 - 60% rel humidity to avoid frost protection, steam injection will offer you less maintenance.
the change over panel is a UK.panel/2skyair used for two units change over but you can parrallell 2 units on each, this will work well.

brunstar

I know the skyair units have had 'computor room setting' setting for a few years now.
my understanding is that it makes for a slightly higher different target evaporating temp & this results in the compressor running at slower speed.
This makes SHF slightly higher.

Are you able to confirm the exact control statagy for these systems using the ' computer room low humidity application' setting ?

What impact have you found this setting to make on the performance & operation of the systems ?

Have you found the systems to have reliable operation & over what period of time ?

I note that you still suggest a humidifier in the room to maintain 50 to 60% RH.
To be sure this is the best method I have found to make improved performance for standard split systems used in computor rooms.

Also I have seen energy heat recovery ventilation system used to good effect.
It brings in outside air which helps with humidity.
It pre cools the outside air when the outside air is hotter than the computer room extract air.
It provides free cooling for most of the year when outside air is cooler than the computer room set temp.

Its a cost effective energy efficient method of improving humidity & reducing the load & run hours of the cooling systems.

Quote:

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Originally Posted by brunstar

Thermatec, for this application you can use 4 x Daikin RZQ100 units which offer low humidity settings for this type of application, you can use a change over panel so that only 2 units run at any one time 2 for master and 2 for slave and change over on a weekly basis, this control system also has an external thermostat so that if the two units can not cope with the load and go into an alarm fault of say 25 degress, what ever you set it up for the second two units will kick in, this strategy will reduce the overall number of starts on all of the units, protecting the compressors.
I would also suggest a humidifyer as to keep the room at 50 - 60% rel humidity to avoid frost protection, steam injection will offer you less maintenance.
the change over panel is a UK.panel/2skyair used for two units change over but you can parrallell 2 units on each, this will work well.

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Isn't that configuration (double capacity and dehumidifier) make costs of instalation and equipment similar to those of close control equipment, and you still doesn't have right equipment for the job.
Not to mention free cooling capability of any decent close control AC.

Check this one!

From the archive

I once had to trouble shoot a VRF system installed in a computor room.

The consultant called for a site meeting with the installation contractor , the maintenance contractor & the manufacturer to try & sort out the poor performance of the system.

The contractors & consultant could not or would not accept that the system would have poor performance below 15 deg C WB.

So we all watched the system performance on the laptop computer monitor for a while.
The humidity in the room made about 12 deg C WB.
The indoor coil temp was below coil frost prevention temp, the suction pressure was low & so the outdoor compressor would not ramp up which resulted in poor cooling performance & high room temperature.
All as expected really but in this case unaceptable for the consultant & contractor who considered this to be a problem with the system operation.

Then we put into the room one 3kw kettle from the kitchen.
the kettle was left to boil with the lid off so that it continued to boil & boil & boil.

Within 10 mins the indoor coil temp improved to above coil frost prevention condition , the suction pressure improved & the compressor ramped up to high speed & for the first time ever the room temperature came down to set point temp.

Suddenly the consultant & contractors realised that the poor cooling performance was due to the low humidity.

Faced with this conculsive evidence all aggreed that the simple soluton was to install a wall mounted humidier.

Problem solved :D

Quote:

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Originally Posted by nike123

Isn't that configuration (double capacity and dehumidifier) make costs of instalation and equipment similar to those of close control equipment, and you still doesn't have right equipment for the job.
Not to mention free cooling capability of any decent close control AC.

Check this one!

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Nike. Have you seen my other thread asking about Hiref products? Have you had any experience with them?

Quote:

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Originally Posted by Thermatech

No problem

I am an independant specialist
I have worked in the ac industry for 32 years
over the years I have worked for a number of major & minor manufactures
in a number of possitions from apprentice technician through to service manager

Now I am semi retired & just work part time
I provide specialist trouble shooting & commissioning assistance to a number of manufacturers, distributors & ac contractors

This issue of small computerroom high sensible cooling load application with standard comfort cooling split & VRF systems is a problem I have had to trouble shoot many many times

Over the years
I have experianced this situation form the perpective of
installation contractor
maintenance contractor
distributor
manufacturer

When any manufacturer can produce a reliable wall mounted split system with high sensible heat capacity of about 10kw then contractors would buy them by the container load.

Untill then most will continue to use standard comfort cooling split systems which are far from ideal for computer room application

---

32 years & semi retired? I've been in 35 years & haven't paid off the mortgage yet! You must have won the lottery along the way or done a whole load of overtime.
Seriously though, I totally understand where you are coming from and agree entirely with your statements. Trouble is small server rooms don't have the budget for "pucker" equipment otherwise that's waht would get installed. Makes me laugh that they can find the money for all the latest blade servers and top of the line rack systems but can't afford the proper cooling system to protect it all. Just like buying a Ferrari and not being able to afford the insurance or fuel!!

I'm trying to find / apply the best cost compromise and I agree that if any manufacturer were to market a system along these lines then they would corner the market in double quick time. Now there's a thought.

Quote:

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Originally Posted by Greengrocer

Nike. Have you seen my other thread asking about Hiref products?

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No I did not! I will check.

Quote:

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Have you had any experience with them?

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I have been in factory and seen production of all their production range 3 years ago. They also produce large chillers for Galletti and I servicing and commissioning Galletti chillers here in my region.
I personally never worked with Hiref close control units, so I don't have any experience in that field yet. From my visit to factory, I got impression that they are solid and that also confirm their reference list.

Quote:

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Originally Posted by nike123

No I did not! I will check.


I have been in factory and seen production of all their production range 3 years ago. They also produce large chillers for Galletti and I servicing and commissioning Galletti chillers here in my region.
I personally never worked with Hiref close control units, so I don't have any experience in that field yet. From my visit to factory, I got impression that they are solid and that also confirm their reference list.

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Many thanks Nike. Their Inverter Close control units are interesting. First full funtion close control Inverter compressor systems I've seen. They even do a small capacity range. Problem is that the prices are very high compared to convensional splits. My search goes on I guess.

Quote:

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Originally Posted by Greengrocer

Problem is that the prices are very high compared to convensional splits. My search goes on I guess.

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That is because they cannot be compared with conventional split units. Check this pdf.

Quote:

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Originally Posted by nike123

That is because they cannot be compared with conventional split units. Check this pdf.

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Couldn't open that link / pdf Nike.

Quote:

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Originally Posted by Greengrocer

Couldn't open that link / pdf Nike.

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Ok. I uploaded it to good server!

http://www.mediafire.com/?rmehgmmdmdw

Quote:

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Originally Posted by nike123

Ok. I uploaded it to good server!

http://www.mediafire.com/?rmehgmmdmdw

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Are they are still using R407c? Surely R410a is the way to go. Having said that some specialist UK manufacturers are still using R407c as well.
Do you kow if they make their own condensing units or do they buy them in from elsewhere?

Quote:

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Originally Posted by Greengrocer

Are they are still using R407c? Surely R410a is the way to go. Having said that some specialist UK manufacturers are still using R407c as well.
Do you kow if they make their own condensing units or do they buy them in from elsewhere?

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From what I saw, they make their own.
For newest technical data I am momentarily unable to attend to their intranet. Probably they will make R407 until they sell all stock (and already ordered) of parts for R407C.

green gracer, the key to all server rooms is humidity and should be applied to all comms rooms regardless.. if you wanted a system to be interlocked with your air con Vam units communicate with their indoor unit and if free outside air is avaliable it will force the compressor of and just induce fresh air.
the other thing that is attractive is humidifyer in the room so that the humidity is kept high and install a vrv heat recovery unit and that heat of rejection and which is recovered from the room can be rejected to a hot water cylinder.
The key again is humidity otherwise the unit will go into frost protection.

i have found that most of the comms rooms i have done were for large companies with multiple racks within, these companies also had excessive back up as they were international companies like visa and 1 minute of servers down would cost millions of dollars so they would spend on the initial outlay but i can understand smaller companies, if they want a cheap high wall to do the job they still should have 2 units with staggered setpoints and humidity control.

Hi Green/ Electro,

Yes Sanyo do not have a 10 KW high wall(despite screaming at the factroy for this) but we use a TDR under ceiling unit as a replacement. I find you get better air distribution in the comms room with this type anyway.

Installing a smaller 10 kw outdoor with a 12 kW indoor is possible with a Sanyo system its an easy adjustment to make.

Don't recode the indoor as this will slow the fan down and defeat the whole purpose of the larger fan coil. set the system to ignore capacity of indoor unt.

It will still control compressor speed based on indoor coil temperatures and the differance between return air temp and set point.

Good look with this what ever units you decide to install

T

Hi Green,

Another option with Sanyo is you can limit the outdoor capacity of a Sanyo System in 5% increments IE you could install a Sanyo system and Limit the actual capacity of the outdoor unit to maybe 85% of its rated capacity.

Switch the system on check air off temps if there to low reduce capacity by another 5 % this may help with the excessive latent cooling.

Your cooling load should be constant so once this commissioning is done once it should suffice.


Or at least until the IT guys install another 10 kws of servers without considering the impact on the A/C

But when all is said and done I do agree with Thermatec Humidity control is the best option here.

T

Quote:

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Originally Posted by techguy

Hi Green,

Another option with Sanyo is you can limit the outdoor capacity of a Sanyo System in 5% increments IE you could install a Sanyo system and Limit the actual capacity of the outdoor unit to maybe 85% of its rated capacity.

Switch the system on check air off temps if there to low reduce capacity by another 5 % this may help with the excessive latent cooling.

Your cooling load should be constant so once this commissioning is done once it should suffice.


Or at least until the IT guys install another 10 kws of servers without considering the impact on the A/C

But when all is said and done I do agree with Thermatec Humidity control is the best option here.

T

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Hi Techguy. Yep I have though of that approach as well for those makes that offer it. 5% increments is better than most other makes.
Is that feature available on Sanyo's splits or just VRF? If so how low can you go / limit the max capacity - 50%?
Given that this would be a permenant set up (and not a time based load shedding or high electric tariff avoidance feature) does it affect oil return or pipe sizing / lengths in any way?

In some ways this would be a better approach since ther are no special mods to do on the mix matched halves of the system. I'm also sure Sanyo distributors would prefer to sell match pairs of systems instead of mix matched - causes all sorts of stock problems.

Think I'll visit Sanyo stand at the RAC later this month. Problem is unless my old buddy GW is on the stand they'll all be sales guys.

HI GG,

It can be adjusted as low as 45% of rated capacity but i would'nt recommend it. Yes both VRF and Splits have ths function.

Regarding pipe sizing most Jananese splits pipe sizing is oversized.

We use the same pipe sizing for a 7.5kw system as a 16kw system.

We use a 3/8 liquid line for a 7.5 kw system and a 28 kw system. So pipe sizing isn't an exact science on split systems. On Vrf systems its a bit differant.

Oil return : It would have some effect as this would limit the speed of the inverter compressor and would result in lower refrigerant flow velocity's. We do have good quality oil seperators in all commercial systems 98% eff(Factory info only have never seen an official doc relating to this). But that last 2% could cause you problems if over time it migrating back to the compressor.

Personally I wouldn't recommend going below 80% of capacity . This is just a limit I have personally set myself.

Do Discuss this with GW at the RAC he should be there but be warned he has gone over to the Dark side. The commercial guys own his soul now.

Tell him T said hello.

Think you will find that Hitachi IVX inverter split & ME Mr Slim inverter split systems have energy save options which limit current to 50% & 70% options.
This option should result in reduced compressor speed & higher evaporating temp which should result in higher SHF & reduced dehumidification.
As both manufactures use the outdoor units as multi split configuration you can install a number of indoor units.

However can the manufacturer provide SH performance data for all the possible indoor unit configurations & energy save reduction fuction ?
Or provide any SH performance data for less than 15 WB ?

I suspect contractor will still end up making a guess for the part load SH performance
& the RH in the room will still get below 15 WB unless some humidity is introduced to the room.