Hitachi Summit 2.5kW Wrong Target Temperatures

[Jimbo!]

Hi all, me again (DIYer) :cool:

I have a new Hitachi DC inverter 2.5kW split, RAS-25.

Problem is that the indoor unit's temperature sensor seems to be a fair bit out. Setting the minimum 16*C heating mode yields a room temp of 19*C.

Is there any way to enter a service mode to apply a correction to it?

Might sound a stupid question, but I ask because I've done exactly that with a Vaillant boiler :)

Thanks!

[Brian_UK]

If you set the heating at 16°C why do you expect it to COOL the room from 19°C ? :confused:

[Jimbo!]

Hi Brian

It's in heating mode, and freezing outside :rolleyes:

[The Viking]

Hi all, me again (DIYer)

Setting the minimum 16*C heating mode yields a room temp of 19*C.


As the unit is in HEATING mode, it will heat up to the setpoint (16), if the temperature get warmer than this, it will not treat the air in any way.

If you want to check the temp sensor when the room temp is 19, then I suggest that you put it in HEATING mode with a setpoint of 22 degrees and measure the temperature of the probe when the outdoor unit stops.


Good luck,

[Jimbo!]

Hi guys

Sorry perhaps I've explained badly. The system is the only source of heat in the building. The set point is 16*C, but the actual room temp levels at 19*C. It is roughly 0*C outside and there are no other sources of energy switched on.

Thanks!

[nike123]

Most of wall split type air conditioners in heat mode actually heat 2-3K more than set temperature to compensate temperature difference between floor and higher part of floor which is normally around 2-3K.
Question is where did you measured temperature.
If you measured temperature at height about 2 meters, and if we consider measuring error both from sensor and thermometer, then consider that your air conditioner works perfectly.
Also, you should consider, that in heating, we have positive temperature differential, which mean, that unit heats to set temperature plus differential (usually 2K) and stops until temperature fall to set point. Then starts again etc...

[Jimbo!]

Interesting. The room temp is being measured at about light switch height, 1200mm, but the air-on temp is actually more like 22*C up by the ceiling.

On full-auto mode, which doesn't seem to have adjustable set points, is heats the room to about 30*C!!

Thanks

[John MacK]

Just to clarify;

your unit is set to Heat, 16 deg.

the room is 19 deg.

the unit is not heating.

That is correct.



You should be able to adjust the temp and fan speeds on Auto.

The unit will then heat or cool as required to maintain the set-point.

p.s. Heat rises :D

[Jimbo!]

Here is the issue.

Heating set to 16*C heats to 19*C.

Hearing on auto (22*C possibly according to the manual) heats to 30*C.

Cooling set to 21*C cools to 15*C.

Surely this is not right.

[nike123]

Here is the issue.

Heating set to 16*C heats to 19*C.

Hearing on auto (22*C possibly according to the manual) heats to 30*C.

Cooling set to 21*C cools to 15*C.

Surely this is not right.

You are right, that is not right. Probably your sensor is wrong, but I see that in few cheap Chinese units before, and maybe you should adapt and learn to live with that.

[Jimbo!]

is Hitachi cheap chineese then :eek:

[nike123]

is Hitachi cheap chineese then :eek:
They have cheap Chinese and expensive Japanese unit as majority of Japanese (and rest of the world) manufacturers have. Did you know that 90% of world production of residential split-system air-conditioners
are made in China.
Where do you think your air conditioner is manufactured?
http://www.hitachi.com/products/personal/home.html#air

[Jimbo!]

Yes, I did know that, by Galanz often. Then so are iPods and an awful lot of silicon related stuff in general.

I thought I was buying a premium brand, not so you think?

[nike123]

Yes, I did know that, by Galanz often. Then so are iPods and an awful lot of silicon related stuff in general.

I thought I was buying a premium brand, not so you think?

How much did you pay? Does that buying looked as great bargain?
Ask that questions your self every time when you buying technical equipment.

[Jimbo!]

it wasn't cheap, £750 ish including pipes etc

[John MacK]

Hitachi are generally a good reliable make.

Have you spoken to the supplier? It does sound like a sensor problem.

[nike123]

Did your aircon have anything to do with theese:
http://tinyurl.com/2ltogn

[nike123]

I thought I was buying a premium brand, not so you think?


Every brand today have products for different markets, and trend is that importers trying to sell huge quantities of cheap products more often than expensive and reliable products. That have something to do with today consumers habits who wants to have everything regardless of quality.

Except mobile phones and cars!;)

[Jimbo!]

I just don't understand this. The specs of this system I think are quite good - R410a, dc scroll compressor, inverter, COP/EER 4.3, 0.9..3.1kW, 20dB indoor, Hitachi with it - and yet it's junk?

[Gary]

Here is the issue.

Heating set to 16*C heats to 19*C.

Hearing on auto (22*C possibly according to the manual) heats to 30*C.

Cooling set to 21*C cools to 15*C.

Surely this is not right.

The sensor seems to be off in both directions, which is not possible.

Keep in mind that the unit doesn't care what the room temperature is, it cares what the sensor temperature is.

For example, if the sensor were mounted on an outside wall: In the winter it would think the room is cooler than it actually is and would overheat the room. In the summer it would think the room is warmer than it actually is and would overcool the room.

Are you measuring these temps at the sensor? Where is the sensor located?

[nike123]

I just don't understand this. The specs of this system I think are quite good - R410a, dc scroll compressor, inverter, COP/EER 4.3, 0.9..3.1kW, 20dB indoor, Hitachi with it - and yet it's junk?

I don't say that. I only know when I got Japanese manufactured unit you could see big quality difference compared to same similar units of same brand but manufactured outside Japan. Also, I know fact that here in Europe, Fujitsu sell units mostly manufactured in China and Taiwan, and in Australia they sell units mostly made in Japan. That practice is widespread between Japanese manufacturers because they have hard time to sell their high quality, high tech products outside Japan (and possibly Australia, and few other "high standard" countries).

[al]

jimbo

We install quite a bit of Hitachi, it's very reliable in general. the problem you are having is that even though the setting can go to 16oC the unit operates to a minimum set point of 19oC, hence the room being at 19oC. Before you go off on one about cheap chinese :eek:tat i seem to remember something similar with other makes also!!

Regards

Alec

[Gary]

jimbo

We install quite a bit of Hitachi, it's very reliable in general. the problem you are having is that even though the setting can go to 16oC the unit operates to a minimum set point of 19oC, hence the room being at 19oC.

Regards

Alec

But that doesn't account for this:



Cooling set to 21*C cools to 15*C.

[The Viking]

One step back....

How long is the unit heating or cooling for?

I.e. How long does it take for it to cool from, say, 24 down to 19?

Or heat from 20 to 25?

[Jimbo!]

Was just trying that actually. So far it's done about 7*C heat rise in approx 10 minutes.

The room is very low thermal mass - insulation is behind plaster board - and there is nothing in it at the moment.h

[borodave1973]

Souds like you have fitted to big a unit for the room:eek:

[The Viking]

Aha!
Jimbo,

Most modern inverter driven units will have some sort of minimum run time....
My bet is that it isn't the thermostat that's keeping the system heating above setpoint (or cooling below...), there is a minimum run time timer and only when that's satisfied will the system notice that the thermostat isn't calling for anything any more...

You could of course put an electrical fan heater in the room, allow the room temperature to rise to 25. Then with the heater still turned on, put the A/C in cooling mode and only after 20 min turn the heater OFF. Then observe the temperature (at the units air intake) when the system stops.

Good luck

[Jimbo!]

Thanks for all the suggestions!

I've made some progress on this which fits with what's been said. The system's heating is 0.9..4.4kW, explaining why it can achieve such quick heat gains.

By setting the fan speed to minimum (auto mode always switches to high when compressor running?) and having improved background ventilation, greatly reducing indoor humidity, the situation is greatly improved :)

Full auto mode still U/S but not a great loss.

And yes, the system was indeed made in P.R.C.

I always knew the heating side was over-sized, but it's practically the smallest system I could find and I wanted good cooling as well (hence not the 1.8kW version).

Finally, does running the minimum indoor fan speed reduce system COP?

[Jimbo!]

Hi All,

Thought I'd give a quick update on this as I've got the service manual from the good folk at Hitachi now :)

As suggested, it does indeed have an minimum compressor run time - 3 minutes.

Also as suggested, the heating temp is +- 0.3K about 3K above the handset set point, so for 16*C it is on at 18.7 and off at 19.3.

By turning the fan speed to minimum the compressor speed has also been limited from its 4400rpm max speed to 2500rpm, bringing with it a similar reduction in capacity and hence improving the overshoot situation :rolleyes:

Efficiency wise it still seems fine - averaging 300W to provide ~18*C rise in a 35cu.m room which has 10sq.m of glazing :D.

Cheers!

Thanks for the input.

[Brian_UK]

Things are improving then Jimbo, good to hear. :)