Humiditys effect on Air conditioning

euser1984

I have a room set to 17c and in the last few days the room is staying at around 18-19c and seems to be still going up.

The only difference is that the humidity has started dropping - it was always around 50% but it's currently gone down to 36%.

I'm not sure why the humidity has changed.

Thanks for any info.

jeepers101

Is there an issue with the fan on the unit?

That would explain the slight increase in room temp and decrease in humidity.

Commercial air conditioning units with a dehumidify function do exactly that. They maintain a full flow of refrigerant through the cooling coil but throttle the fans down to ~half speed.

Now that I think of it have you checked to make sure its on the correct mode? What's the make and model of the unit?

euser1984

The fans seem to be ok - it is blowing air from the indoor unit at a good fan speed and the outside fan seems to be working fine.

The model of the indoor unit is SM802KRT-E (Toshiba), do you need the model of the outdoor also (lashing rain when I just opened the door to go outside). It is on chill mode (snowflake) and the flap is at the top position.

Hope you can help...

jeepers101

No, don't need outdoor model. That indoor is a wall mounted unit iirc.

A nice and easy way to check for adequate gas charge on a wall mounted unit is to put your hand up and feel the airflow from the unit. Start on the right and slowly move left.

The air should feel cold the whole way across. If it starts to feel warm towards the end then a likely cause would be a gas shortage. If it is warm towards the left side go to the outdoor unit and check the two pipes. Feel the larger pipe. It should feel cold while the system is in cooling mode and if not lagged could possibly even have condensation on it.

A sure sign of a gas leak on these units is the presence of refrigerant oil. The most likely places for a leak is around the flare nuts. You'll find the flare nuts where the pipe connects to the unit; both indoor and outdoor. You can't miss them, they look like brass nuts. Indoor flares can be hard to access but the outdoor flares can be easily got to by removing the cover held by a single phillips screw.

If you have a decent thermometer check the off coil temperature (the air blowing out of the indoor). You should be getting about 8 degrees the whole way across.

Just out of curiosity what kind of room are you trying to keep cool? Wine cellar?

euser1984

jeepers101 wrote: »

No, don't need outdoor model. That indoor is a wall mounted unit iirc.

A nice and easy way to check for adequate gas charge on a wall mounted unit is to put your hand up and feel the airflow from the unit. Start on the right and slowly move left.

The air should feel cold the whole way across. If it starts to feel warm towards the end then a likely cause would be a gas shortage. If it is warm towards the left side go to the outdoor unit and check the two pipes. Feel the larger pipe. It should feel cold while the system is in cooling mode and if not lagged could possibly even have condensation on it.

A sure sign of a gas leak on these units is the presence of refrigerant oil. The most likely places for a leak is around the flare nuts. You'll find the flare nuts where the pipe connects to the unit; both indoor and outdoor. You can't miss them, they look like brass nuts. Indoor flares can be hard to access but the outdoor flares can be easily got to by removing the cover held by a single phillips screw.

If you have a decent thermometer check the off coil temperature (the air blowing out of the indoor). You should be getting about 8 degrees the whole way across.

Just out of curiosity what kind of room are you trying to keep cool? Wine cellar?

What does refrigerant oil look or smell like? I just checked the flare nuts outside and there is something that may be a little greasy, but very little and, with no smell.....it is wet around that area but I'm assuming that's just water from the rain (high winds here also). The large pipe does feel cold.

The temperature does seem to be the same if I move my hand over from right to left on the indoor unit...I don't have a proper thermometer but it seems to be about 6.5 to 6.8c across with around 70% humidity...

I'm running a few hot computers for work in my house...using up about 4kW of power.

jeepers101

euser1984 wrote: »

I'm running a few hot computers for work in my house...using up about 4kW of power.

Ah okay. For starters your set point is far too low for that kind of application. I've looked after air conditioning units in large data centres and its not uncommon for them to be set at 24-26 degrees. They incorporate a hot aisle/cold aisle system where they set all the server stacks up in rows so all the server hot air is exhausted in the same direction to every second aisle. Then they build enclosures around the cold aisle and pump the cold air into it. The hot aisles in this situation can get up to around 35 degrees.

I would recommend increasing your set point to around 23-24 degrees. Modern computer equipment is rated to withstand far hotter than that. Also humidity has little effect on the newer equipment.

The problem with having your set point so low is that your unit will never actually be able to achieve it. Mitsubishi units don't actually allow you to set them any lower than 19 degrees. Having a set point of 17 degrees in a computer room means your unit will constantly have cold refrigerant pumping into your cooling coil. This will result in a lot of condensation. You can see this yourself if you check the outlet for the drain. You will likely see a constant drip from it. This can be especially detrimental for Toshiba wall mounted units. There was a large batch of Toshiba wall mounted units released to the market a few years ago with cooling coils that fail under this very condition. I've had to change a few of them. It can be expensive enough.

You'll also save money on your ESB bill if you increase the set point.

As for why the room temperature has increased a couple of degrees I'm not entirely sure. The off coil temperature seems good and the cold suction pipe would be a rough indication of good superheat. I assume you've checked the indoor filter??

WRT the oil, it would be quite noticeable if you had a leak. It would be like someone poured a little bit of olive oil over your flare nut. It does have a distinctive smell but I couldn't describe it. Sounds to me like the system is running fine and in that application (computer room) I wouldn't be worried about that kind of fluctuation in humidity, especially as you have no humidity control. If you are concerned about it, buy a humidifier. They're fairly inexpensive.

Borzoi

jeepers101 wrote: »

Ah okay. For starters your set point is far too low for that kind of application.

The problem with having your set point so low is that your unit will never actually be able to achieve it. Mitsubishi units don't actually allow you to set them any lower than 19

Agreed most data centres are set for 20-22c which is fine.

It may also be that your system is not suitable for use as a comms room set up. Many of the "domestic" ranges are not rated to provide cooling when the outside temperatures are low, which they are now.

jeepers101

Borzoi wrote: »

It may also be that your system is not suitable for use as a comms room set up. Many of the "domestic" ranges are not rated to provide cooling when the outside temperatures are low, which they are now.

Not true at all. In cooling mode your outdoor unit is acting as a condenser. Low ambient temperature will have no effect on a system with an inverter driven fan such as this. His system is more than adequate.

And you may find over cautious IT people setting air conditioning down to 20 degrees in some smaller comms rooms but in large data centres they wouldn't waste that kind of money.

Borzoi

jeepers101 wrote: »

Not true at all. In cooling mode your outdoor unit is acting as a condenser. Low ambient temperature will have no effect on a system with an inverter driven fan such as this. His system is more than adequate.

I suggest you look at a Mitsi data book before making such blanket assertions. Some of the smaller m-seies are restricted with temperature range. I'm not familiar with Toshiba equipment but its likely similar, because the same applies to several other big names.

jeepers101

Borzoi wrote: »

I suggest you look at a Mitsi data book before making such blanket assertions. Some of the smaller m-seies are restricted with temperature range. I'm not familiar with Toshiba equipment but its likely similar, because the same applies to several other big names.

M-series outdoor operating range is in the region of -10 to 43 degrees. So is Toshiba's. The weather this winter has barely dropped below 0. I fail to see your point here.

euser1984

I have tried different temperatures and it won't fit any temp properly - at the moment it's set to 20c and the thermometer is showing 18.4....

The humidity seems to be in or around 50% all the time again, even though I know you said this isn't an important factor. I know what your saying about the hot aisle/cold aisle system as I've heard about it before....do you think that could be the problem in my room?

jeepers101

euser1984 wrote: »

do you think that could be the problem in my room?

Definitely not. I was just trying to highlight the acceptable temperature range in the industry.

To me it seems your unit is working perfectly fine. You do not have a close control unit. You have a split.

I would often find small computer rooms served by a similar unit to your own set at 19 degrees but have a room temperature of 16 degrees.

The reason for this could be any of a number of the following or another reason I haven't thought of.

- The air conditioning return air temperature sensor is out of calibration
- Your thermometer is out of calibration.
- Your thermometer is located near the off coil air flow.
- The hot air from your computer equipment is very near the unit.
- (Most Likely) These air conditioning units have a proportional band built in, which means they'll cool a certain amount lower than their set point, then ease off.

Don't worry about a difference between the set point and your thermometer reading. If you find that a desired set point of 20 degrees is giving you a room temperature of 18 degrees, simply increase your set point to 22 degrees.

euser1984

jeepers101 wrote: »

Definitely not. I was just trying to highlight the acceptable temperature range in the industry.

To me it seems your unit is working perfectly fine. You do not have a close control unit. You have a split.

I would often find small computer rooms served by a similar unit to your own set at 19 degrees but have a room temperature of 16 degrees.

The reason for this could be any of a number of the following or another reason I haven't thought of.

- The air conditioning return air temperature sensor is out of calibration
- Your thermometer is out of calibration.
- Your thermometer is located near the off coil air flow.
- The hot air from your computer equipment is very near the unit.
- (Most Likely) These air conditioning units have a proportional band built in, which means they'll cool a certain amount lower than their set point, then ease off.

Don't worry about a difference between the set point and your thermometer reading. If you find that a desired set point of 20 degrees is giving you a room temperature of 18 degrees, simply increase your set point to 22 degrees.

That is good to hear....

Is the temperature sensor in the remote controller, or the "indoor unit" return/hot? air intake?

jeepers101

Is it a hard wired remote or infrared?

euser1984

Infrared...

At the moment it's now showing 19.7 and 40% with the temperature being set @ 20c.....

jeepers101

Yep that all sounds spot on. Don't be afraid to increase that set point.

Your temperature sensor is mounted near the indoor coil. If you lift the cover and remove the filters you should be able to see it.

euser1984

jeepers101 wrote: »

Yep that all sounds spot on. Don't be afraid to increase that set point.

Your temperature sensor is mounted near the indoor coil. If you lift the cover and remove the filters you should be able to see it.

So do you think it was just a case of the temperature being too low? I may experiment with higher temperatures over the next few days.

I forget now again but how many kW's should the unit I have be capable of cooling?

Thanks.

gctest50

euser1984 wrote: »

....using up about 4kW of power.

OT - with the weather the last few days - have you "enough" UPS for them ?

euser1984

gctest50 wrote: »

OT - with the weather the last few days - have you "enough" UPS for them ?

It's no big deal if the machines have to go off for a short while - they will automatically shutdown at a certain temperature.

gctest50

OT :

Oh sorry I meant sudden power cuts because of ESB network problems



https://www.esb.ie/esb-networks/powercheck/

euser1984

gctest50 wrote: »

OT :

Oh sorry I meant sudden power cuts because of ESB network problems



https://www.esb.ie/esb-networks/powercheck/

No power cuts for us thank god (touch wood). The computers are connected via the same supply as the aircon anyways.

jeepers101

euser1984 wrote: »

So do you think it was just a case of the temperature being too low?

Yeah more than likely.

euser1984 wrote: »

I forget now again but how many kW's should the unit I have be capable of cooling?

You can check this yourself on the outdoor unit. Find the label on the front with the model number. It'll have different kw ratings for a list of different indooor units. Just check the one that matches your indoor model.

euser1984

Generally speaking what is the most amount of power available in a domestic setup. i.e. - how many amps can you get?

euser1984

Sorry after some rooting around (alot) I see it's about 12kW.

Borzoi

jeepers101 wrote: »

M-series outdoor operating range is in the region of -10 to 43 degrees. So is Toshiba's. The weather this winter has barely dropped below 0. I fail to see your point here.

ORLY??