Newly installed ducted heatpump system driving us mad

Forums › Home Workshop DIY › Newly installed ducted heatpump system driving us mad - noise and temps

gedc

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#173759 4-Jun-2015 23:21

Hi Folks

Just looking for some advice and or pointers from people who either own one of these or who install them. I'm not looking to crucify the company we purchased and installed through as they are doing all they can to fix the issues to the best of their ability ( but this is one of the first ones they have put in) and we've also had technical reps from the unit manufacturers - fujitsu into the house on 3 occasions in the last 2 weeks to ascertain what's not working. Again, they are doing their best but with most problems and wider audience experiences I'm hoping we can shine additional light on the issues.

It's a whole house system split into two zones. That means 2 large outdoor units and 2 indoor air handling units in the ceiling space - each supplying air to the it's own zone through flexible ducting. There is an air return in each zone and various sized outlets. The zones are split into the 2 x living as zone 1 and the 5 bedrooms, long hallway as zone 2. This system was to replace several individual heatpumps and should have provided whole of house heating.

We appear to have several issues.

1) The air handler units are 'hung' from the trusses in the roofspace on threaded steel rods. I presume to isolate them as much as possible. They are big units and even with the best of intentions may be touching wood in some places. Installer confirmed this. They are also about 4 inches above the plasterboard ceiling. They run on 4 speeds. At speeds 3 and 4 the noise - mainly fan noise I presume is certainly very noticeable but does mainly reduce a fair amount at speeds 2 and 1. Several times a week we get a very loud and noticeable low frequency "hum" in the living areas when it's running - irrespective of the fan speed. As you walk around the living room the hum becomes appreciatively louder then fades away to almost nothing based on where you stand. Reminds me of school experiments and sounds waves doubling in amplitude or cancelling each other out from two different stereo speakers etc. Any ideas what's causing that?

2) There is surging when the unit is running. The fans ramp up and " blow " loudly through the outlet vents, then suck loudly back in through the air return in the ceiling space..Then ramps down, ramps up and repeats. Initial fix was to install larger air returns and straighten some of the tighter bends in the flexible ductwork. That didn't resolve it. Next fix is to install additional air returns in each zone as it appears the volume of air the return can deliver back to the handler is less than the volume the air handler can expel. Sounds plausible but prior to chopping more ceiling space out just wanted some thoughts.

3) The last issue is for zone 2 - the hallway with bedrooms coming off it. There are no outlets in the hallway and the idea is the heat from the bedrooms gets sucked out , flows up the hallway, into the return air vent at the end, through the handler, reheated, then back into the bedrooms, then into the hallway etc. Doesn't quite work like that in principle. What we end up with is two different issues - Temperature layers and generally poor heating across the rooms.

We notice in each room 3 distinct and easily measurable temps - super hot at the top, very cold at the bottom and mildly warm around waist height. Moving from rooms to the hallway and back again, you notice large increases or decreases in temps. You also notice a very hot head as you pass through each bedroom doorway which tells me the return is sucking high level / hot ceiling air back into it.

The second issue is the hallway and rooms don't appear to be heating. Last sunday when it was very cold outside we had the system running all day at 24 degrees on the controller and temps in the bedrooms barely got to 14 to 15 degrees C. Temps in the hallway were cooler. Electricity bill for one day was $37....!!! Shut any bedroom door and that room heats up to HOT HOT within 5 minutes so it appears something to do with the hallway and having the doors open for return air flow.

To me it appears that the forced air from the ceiling is not moving the cold air sufficiently, is subsequently being sucked back into the air return as it's highest level and spewed out again then repeated. I presume eventually it would displace enough cold air but instead of the claimed 20 minutes to bring it to temp its more like 20 hours.

Appreciate you reading and looking forward to moving this onto a better platform.

Thanks again

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#1317627 4-Jun-2015 23:37

Just a thought on number 1. It sounds like you may be on the right track.

2 units running at a slightly different frequency in the same space (you said both were in the roof?) could, quite possibly, create constructive/destructve interference (as you say, the school experiments).

If they're working harder as well due to the issues with air inlet capacity, this may well be a contributing factor.

Just a thought.

gedc

355 posts

Ultimate Geek

#1317629 4-Jun-2015 23:49

Thanks for that. The air handler units in the roofspace are a good bit apart - different ends of the house. he hum comes and goes. Pretty sure it's directly related to the upstairs unit. It's one of those noises that will drive you mad. I can live with a fan noisily blowing air but this background hum is making me potty. Not loud just very evident, particularly moreso when you press the off button.

Cheers

Batman

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#1317651 5-Jun-2015 07:06

How many kw is your headunit

andrewNZ

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#1317654 5-Jun-2015 07:18

The bedroom issue sounds like a lack of air circulation. I'll bet if you put a fan in the room and point it upwards, the room will heat up nicely. I get the same problem in my house with a fire, hot up high and cold down low. I use a floor fan pointing straight up to stir up the air and the heat evens out pretty fast. It also means I have to turn the fire down.

My opinion on the hum is that the units aren't properly isolated from the framework. I'm not convinced that steel rod is going to isolate it properly, but it might.
If the unit/s are touching timber, that needs to be fixed. If nothing else you can cross it off the list of possible causes.

gedc

355 posts

Ultimate Geek

#1317656 5-Jun-2015 07:26

Hi all

Size of outdoor units are 11kw heating. They should be ample for the space according to the tech. I also agree its an air circ issue in the bedrooms and hallway so have asked for the system design to be checked.

Re the threaded steel rods...i also thought they would transfer noise but apparently its the way its done..the fujitsu website did have pictures of their air handlers hanging from wires however. ;)

Keep em coming..we are all thinking the same things

Cheers

timmmay

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#1317663 5-Jun-2015 07:47

My old DVS unit hangs from chain. Given the issues you're experiencing I'd definitely be isolating it better, even if it means significant work. Even finding some heavy duty rubber isolation mechanism may be necessary - like industrial strength rubber bands.

Definitely sounds like the bedroom air needs to be mixed better. Perhaps a different diffuser design that allows more air to go straight down? It doesn't sound practical to put a fan in each room, plus fans add noise. I guess the thing to avoid is drafts people can feel.

I suspect fix those two issues and you'll be much happier.

k14

629 posts

Ultimate Geek

#1317666 5-Jun-2015 08:00

If you don't mind my asking, how much did the whole system cost to install?

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gedc

355 posts

Ultimate Geek

#1317677 5-Jun-2015 08:15

Thanks for those ideas. I think there is a spring type unit that can help in the isolation. I'll chat to the company re them. I also think we are hearing the upstairs air handling units through the return vent and also through the ceiling gib so was wondering re some acoustic dampening material that can be laid over the trusses / insulation upstairs.

RRP for this system was about $27K +/- 3K from several different suppliers. I paid around 20K given I had some personal contacts etc with this company. Still a shedload of cash however for something that doesn't work very well !

timmmay

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#1317688 5-Jun-2015 08:22

I assume you have good insulation between the ceiling and the units? That's essential.

Aredwood

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#1317696 5-Jun-2015 08:32

What is your stud height (ceiling height)? And are the air returns cut into the ceiling? And where are the thermostats located?

RunningMan

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#1317706 5-Jun-2015 08:49

Had a few similar issues when we had a system installed a couple of years ago - in no particular order:

1) Hanging from threaded rods is fine, but the unit must be precisely levellled - if there's too much tension on one corner the unit will twist and vibrate. Must make sure that it isn't touching the framing anywhere or the noise will be crazy high. Also put your hand on it when running to see if any of the steel panels are drumming - a bit of high density foam may deaden this.

2) In your bedrooms, I'd have a supply and return vent in each room, otherwise it'll never work with the doors closed, and will be erratic depending on what doors are open.

3) You can get supply vents with a mechanical thermostat that changes the air supply direction - down for hot air and sideways for cold so that it mixes in to the room properly.

4) Are there seperate dampers on each supply outlet plenum? You will need these to adjust the airflow to each room to get it balanced for room size, heat loss and length of ducting.

5) Thermostat - gave up using the thermostat in the ceiling unit - had it reprogrammed to use a thermostat in the wired remote control pad and it gave far better results.

6) Fan speed - generally set it to a low position and leave it - full speed is noisy and OK for makeing quick changes in temperature, but not needed most of the time.

7) Remember the system needs to move air from one vent to the other (supply to return) so they need to be at opposite ends of the area you are heating - there doesn't need to be a howling gale, but unless there is that gradual movement from one to the other, you'll never get close to an even temp.

gedc

355 posts

Ultimate Geek

#1317720 5-Jun-2015 09:01

Everyone. Thanks heaps.

To answer in rough order

Ceiling is insulated and stud height is standard 2.4m. Air returns are cut into ceiling - currently one air return for each zone. The living room air return suck from both living rooms. The back house air return is at end of long hallway and basically should suck the air from the bedrooms up along the hallway to heat it up. We haven't done this yet but have been asked to cut 20mm off the bottom of doors to allow for airflow if the doors are shut. To date, the doors are always wide open. The thermostats/ controllers are located on the wall almost directly underneath the air returns. Have since been told they shouldn't be there. Temps can be set to be read from the upstairs unit or the wall controller.

Running Man - thanks again for all your comments - I've asked them to recheck the rods issue and I know the units are very tight up there. Once installed they had to climb over one of them several times and the guy who installed it said it was 'just' touching some wood.

I've just had a call from the company ( who are indeed bending over backwards to get this fixed ) and they have engaged a third party to check the design layout, specifications and calcs for airflow etc. They have confirmed this will be put right.

Dingbatt

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#1317721 5-Jun-2015 09:05

Fans in these units are normally high volume low pressure rise designs which are likely to be adversely affected by incorrectly designed ducting. Any sort of back pressure on the outflow side or choking on the inlet will cause the fans to stall and surge which may explain the whooshing you experience from the unit. Flexible ducting is notoriously difficult to calculate flows for because each twist and turn introduces new for characteristics. Larger inlet ducting is a good start.
They have probably tried it already, but have the installers tried running the unit with either the inlet or outlet ducting disconnected? Or even with a length of straight ducting connected to isolate whether the surging is caused by inlet or outlet.
As mentioned above, the heat layers would tend to indicate that the incorrect diffuser design, size or flow rate has been used.

I know it is no solace to you but as you can see there is quite a bit to tuning a system such as yours that is starting to get complicated. But if you intend to use the air-conditioning side of things in summer then the air pooling that is causing problems for heating will work in your favour for cooling.

Edit: Oops I see RunningMan answered most of your queries while I was formulating my reply. Endorse his comments. I am glad to see the installers ate proactive in helping resolve your problem.

“We’ve arranged a society based on science and technology, in which nobody understands anything about science technology. Carl Sagan 1996

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#1317727 5-Jun-2015 09:12

I would think it's the head units causing the hum not the ducting.

RunningMan

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#1317728 5-Jun-2015 09:14

If it were me, I'd ask for seperate return vents in each bedroom, rather than creating gaps under the doors - for a couple of reasons:

1) Leaving a door open or closed will have a very significant effect on airflow for that room, meaing the other rooms also get more or less air. The result is one person opening their door (and allowing more airflow) effectively lowers the airflow to the other rooms meaning less heating (or cooling) for those rooms. It's too easy to muck with the airflow and that's when you end up with uneven temps. These units generally only have one fan, not a seperate fan for each outlet, so the airflow will take the path of least resistance. If that path is easy to change (by closing or opening a door) then it affects airflow through the entire system.

2) Think about when you are not running the system - do you want a big gap under each door? It can be unsightly, create unwanted draughts and let more noise through.

It's a little more complex to install additional return vents but I really think it's beneficial - it's not like you're spending $50 on a cheapo heater - you'll be disappointed spending that amount of money if it isn't the best it can be.

If there's any suggestion at all that the ceiling unit is rubbing on the framing, this has to be sorted - it'll transfer an enourmous amount of unwanted noise if it is touching.

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