Is it possible to overrun the max piping length

[back2space]

Evening all, a little something I would like some help on if any of you wouldnt mind:

Our LG system we cannot afford to replace with mitsi equipment now so we will have to grin and bear its weird control strategy and hope that a 3rd unit may make it run better as a system, however we are getting closer to winter and require heating in another room as cheap as poss without resorting to fan heaters.

OUr washing machine is also on the blink so that is going to need replacing so the money we had saved up to upgrade the system is going to have to be used elsewhere whilst getting another unit added onto our existing system with a small portion of that money.

Our outdoor condenser multi split unit has a max interunit piping length for one room as 25 metres.

However we want to add a unit onto the multi unit and we have measured the distance from indoor to outdoor unit and its actually near to 32 metres.

Is this potentially do able still? Is the 25metres stated by manufacturer just a safe limit.

We are adding a 3rd unit onto LG FM25AH its the best solution for heating and we can get the indoor unit for about £100.

The setup is

3.9kw in lounge (already fitted maintained 23C)
3.9kw in main bedroom (already fitted maintained 19C)

3rd proposed unit is a 3.9kw unit in other day/evening room (to be maintained 23C)

1st 2 units are massively oversized by original installer, and they cope well in winter on really cold days as we have the extra capacity needed for cold days.

Actual sizing of units if sized exactly would have been 1 x 3.9kw and 2 x 2.3

Outdoor unit output is 32000btu in heating.

However fitting a 3rd 3.9kw unit will take the outdoor over capacity meaning shared output to each unit is 9600btu if all are running at same time flat out in heating.

Cooling is not an issue as very rarely will they all be run at the same together in cooling however heating they will be run together but only two will be set at equal set points as are in occupied rooms so set points in these 2 rooms are about 23C whereas one of the rooms is maintained at 19C being a bedroom so this unit will not be in operation long.

Any help as always appreciated.

Looking forward to your advice.

Richard.

[beagle]

Some "safety margin" is built into factory recommended pipe lengths (usually somewhere around 10%) you've got an increase of almost 22% though, little too much in my opinion. Check, check and double check with your supplier though, warranty is their concern and they will say yay or nay.

[back2space]

Equipment is nearly out of warranty.

[hyperion]

If you proceed with a third 3.9kw unit, you will have increased to total heat load to 11.7kw which is 25% above the maximum output of the unit. This will mean that you will not achieve good temperature response under full heating demand in the winter. If you were to obtain a 2.3kw unit and fit this in your bedroom, this would then give you the 3.9kw unit for use eleswhere. You would only then be about 10% over capacity.
With regards the additional piperun, you will probably be reducing the overall efficency of the unit, particularly in times of maximum demand.
No easy solution, particularly in view of financial restrictions.
Proceed with caution or you may find that the system only sort of works and could then be good money wasted.

[back2space]

The thing is the max load even in the rooms with the 3.9kw units in is still only about 2.3 kws so even though there is 3.9kw capacity units the ones that are oversized probably only use a bout 2.3 of that capacity mostof the time so does this still not mean I can put a 3.9kw unit on?

[stefs_cruiser]

Why do you insist on doings things against the manufacturers recommendations?

By your own admission it was oversized, you blamed the manufacturer for bad controlls etc, and now you wish to exceed the pipe run, if it fails, will you blame the manufacturer again??

[back2space]

We have measured the pipe run and have found a differnt way to lower the pipe run to 21mtrs so this way will be fine.

Its not that I insist against manufacturers advice. Its a/c engineers one tells you one thing that it will be ok the other says it wont? Who do you believe?

I still do think its a terrible piece of kit and would never buy it again if I was putting a new install in, however got to make the most of what I have at the moment and money is tight.

It was not my own admission that it was oversized it was the installer who thought best to put a larger unit in for extra capacity due to leaving internal doors open etc and if having friends or parties.

[beagle]

Its not that I insist against manufacturers advice. Its a/c engineers one tells you one thing that it will be ok the other says it wont? Who do you believe?



In a word, the manufacturer.

They spend years and millions developing this kit, their parameters are there for a reason and while you may be able to juggle some of their recommendations around to suit a particular application you need to have the back up of someone that really knows the kit intimately, which in the case of LG isn't an easy thing to get in the UK.