30% rule on City Multi

[Daz man]

Hi guys,

I may have this wrong, but I'm sure Mitsi once explained this to me.

On a R407c City Multi VRF unit am I right in thinking there is such a thing as the 30% rule?

where as there has to be a minimum of 30% of all indoor units running at the same time?

I remember once having a 1501 fault code showing and I was convinced the gas charge was fine so after speaking with Mitsi they explained it may not be a charge issue more a capacity issue, is this 30% rule correct?

thanks

[install monkey]

yep all vrv,vrf dont recommend fitting indoors in server rooms as when the office area shuts off you run a 5 kw indoor with a 30kw outdoor- as an example

[install monkey]

had a mhi kx4 vrf - installed in an office, not by me- does training rooms ,office,mail room and a server room- indoor unit run hours training rooms 600hrs ,1500hrs in the offices,25,500hrs in server room, 600 hrs condenser run time- no alarms and its been in 3 yrs- cant get how many compressor starts its had

[Asbolute]

had a mhi kx4 vrf - installed in an office, not by me- does training rooms ,office,mail room and a server room- indoor unit run hours training rooms 600hrs ,1500hrs in the offices,25,500hrs in server room, 600 hrs condenser run time- no alarms and its been in 3 yrs- cant get how many compressor starts its had

ditto this, keep VRV/VRF out of server rooms. They don't like them! Also, why risk a VRV/VRF operating 24/7 on low load decreasing life expectancy when a split will do the job and less expensive when it fails! Beyond me, the joy of sales

[r.bartlett]

ditto this, keep VRV/VRF out of server rooms. They don't like them! Also, why risk a VRV/VRF operating 24/7 on low load decreasing life expectancy when a split will do the job and less expensive when it fails! Beyond me, the joy of sales

Toshiba happily recommend their VRF for server rooms and run one indoor unit no problem. The heat recovery side will help running costs, improve heat recovery and provide 'free heat' to the rest of the building during the cooler times.

We have a customer who run their server room with 70kw of splits. The DO office directly above has 85kw of splits .... Heat recovery at a 27c (hot aisle) 24/7/365 against fluctuating outdoor ambient. Think of the energy saving during the winter if a VRF install could had been planned from the start?

The old reason for the non recommendation was oil return and defrost cycle would leave the server room open to temperature fluctuations. The latest generation of VRF are more than able to cope with server rooms conditions due to their improved oil return and defrosting.

The only possible downside is that it's not a dedicated system but a well installed well maintained vrf should be pretty much as reliable as a split

[Asbolute]

Toshiba happily recommend their VRF for server rooms and run one indoor unit no problem. The heat recovery side will help running costs, improve heat recovery and provide 'free heat' to the rest of the building during the cooler times.

We have a customer who run their server room with 70kw of splits. The DO office directly above has 85kw of splits .... Heat recovery at a 27c (hot aisle) 24/7/365 against fluctuating outdoor ambient. Think of the energy saving during the winter if a VRF install could had been planned from the start?

The old reason for the non recommendation was oil return and defrost cycle would leave the server room open to temperature fluctuations. The latest generation of VRF are more than able to cope with server rooms conditions due to their improved oil return and defrosting.

The only possible downside is that it's not a dedicated system but a well installed well maintained vrf should be pretty much as reliable as a split

I've monitored VRV/VRF data whilst recording overnight on a number of occasions and the low humidity tends to drop the back pressure and increase the discharge temperatures, system would enter internal safety devices and you have no cooling what so ever. During office hours tends to be ok but the compressor is always thermostat ON and we all know how much these cost to replace and we also know that the more the compressor operates the less life. Splits for me and would be happy if get 6yrs out of splits in server room. The majority of the time the customer can replace a split system a lot cheaper than replacing VRV/VRF compressor plus you have a whole system down whilst replacing VRV/VRF compressor

[r.bartlett]

I've monitored VRV/VRF data whilst recording overnight on a number of occasions and the low humidity tends to drop the back pressure and increase the discharge temperatures, system would enter internal safety devices and you have no cooling what so ever. During office hours tends to be ok but the compressor is always thermostat ON and we all know how much these cost to replace and we also know that the more the compressor operates the less life. Splits for me and would be happy if get 6yrs out of splits in server room. The majority of the time the customer can replace a split system a lot cheaper than replacing VRV/VRF compressor plus you have a whole system down whilst replacing VRV/VRF compressor

Which VRF were you monitoring

I also tend to disagree with a 6 year life as that's not my experience.

[install monkey]

the issue of diversity will also affect your server room- server room set for typically 19 cool or as low as the IT gimp can set it, middle of summer and your office is set to 25 heat (dont get sun in manchester- a heatwave is anything over 11 deg), you gonna lose capacity as the units cannot give their rated duty, also as prev mentioned when ur vrv,vrf faults your servers cook, servers go down
sanyo did do a celler cooler for their vrf system

[Asbolute]

Which VRF were you monitoring

I also tend to disagree with a 6 year life as that's not my experience.

Mitsubishi and Daikin, as a rule i'd try to avoid server rooms but that is my experience with them, however I do see them a lot in server rooms.