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  # 1317732 5-Jun-2015 09:19
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An example of a thermostatic diffuser - directs airflow vertically when hot air is flowing and horozontially when cold.

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  # 1317745 5-Jun-2015 09:36
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I would have thought hot air from bottom. Vents at the top, directly opposite from the entry. Physics.

Swype on iOS is detrimental to accurate typing. Apologies in advance.


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  # 1317747 5-Jun-2015 09:40
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1   Vibration isolation in HVAC can be bit suck-it-and-see, but good practice in systems which need to be quiet (eg residential) would be to have vibration isolators on the hangers.  Plus make sure nothing is touching the structure anywhere.  This may not the problem, but it's the most likely fix.

2   Surging on the air side usually means the fan is not suitable for the duct system.  If the air flow resistance downstream (filters, ducts, grilles etc) is too high then the fan operates at the top of it's curve where it's unstable.  It sort of goes into an out of stall.  When this happens you get surging and substantially reduced air flow and capacity.  The solution is to have the fan and ducts properly sized.  But you could also look for anything creating a high resistance in the ductwork, like kinks in the flexibles or something obstructing the filters etc.  Also make sure the grilles are not throttled off (at least one of them should be fully open).

3   You don't say clearly, but if air is supplied to the bedrooms and returned via the hallway then you need transfer grilles (usually in the doors) if you want the system to work with the doors closed.  The stratification you describe is poor air diffusion (the way the grille/diffuser mixes the air in the space), and is caused by the air flow being too low for the grille/diffuser.  A grille has to "throw" into the space at a certain velocity to generate proper diffusion.

The first step to checking out 2 & 3 is to measure the air flow at each supply grille, add them up and plot it on the fan curve.  If your installer is a newbie he might struggle with this.


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  # 1317973 5-Jun-2015 15:28
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Pretty much everything I was going to add has already been covered. But main thing is definitely move those thermostats. The one that is in the hall needs to be moved into 1 of the bedrooms. (most likely master bedroom). As the hallway is the worst possible place for a thermostat. By the time the hallway is warm enough for the thermostat to reach the set temp. The bedrooms will be way too hot. And after the thermostat has switched off the heat. The hallway won't cool down much until the bedrooms have cooled down. So the thermostat won't know that the bedrooms need more heat until they are cold. Which means you will get big temp swings.

Before getting the return air ducting changed (cutting more holes in the ceiling). Move the thermostat to 1 of the bedrooms, close the bedroom doors, set the fan speed to high, and give the bedroom unit a test. As you have multiple issues. But some of them could just be symptoms instead of actual install / setup problems.

Personally I think the biggest issue is just thermostat location. Because the OP said the bedrooms got too hot with the doors closed. There is definitely enough heat able to get to the rooms. And my suspicion is that the fan surging is the indoor unit sensing that the return air is hotter than the temp that the thermostat is reporting. And is then going into a "overheat mode" (no heat, max fan speed) The return temp will then drop so it will go back into normal mode. And then the cycle will repeat.

Also you should consider having the return air inlets relocated to floor level. (would most likely mean that the return duct will need to run down inside a wardrobe or cupboard). So they are drawing in cold air at floor level. This would also help to increase the efficiency of the heatpumps as they will have colder air going through the condenser.

[Edited to add]

What height above the floor are the thermostats installed?

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  # 1318096 5-Jun-2015 17:11
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What part of the country are you in? Try asking on this forum


Ducted heat pumps are rare in NZ but common in Australia so there should be installers there who may give you insights. There are also forums dedicated to air conditioning users.



gedc: 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.



All houses have heat entering them through the windows so it makes sense the reason we need heating is because of heat escaping. The more rapidly heat escapes a house, the more thermal layering may happen when a heater is at work, except possibly with underfloor heating. While the ducted system may be set up wrong I do wonder about how well insulated the house is? Until recently, houses didn't have much in the way of wall insulation and the building code still doesn't require much underfloor. Older insulation in ceilings was inadequate and usually used materially which degrades in effectiveness over time.



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.

4kw/h for 24 hours is a big heating load. Unless you're living in Invercargill under the shadow of a tree I don't think a room temperature should be dropping so low with no heating going on. Does the ducted system have an HRV system integrated with it?

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  # 1318466 6-Jun-2015 22:25
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we have a fujitsu ducted system, its an 14kw single unit with 2 outside units powering it our place is about 170m2 excluding garage,
and yes the rooms do heat better when the doors are closed for the simple reason that the air can only return under the door so the room "fills" with warmer air. if the door is open the warm air simply spills out the room at the top of the door back to the air returns in the hall.
 as ours was a new build, all the doors were trimmed shorter at floor level to allow for airflow when closed. we have 2 return air grates at floor level, one for the lounge and one into the hall. the return air suctions are in the hall in the ceiling.
  The air vents into your rooms should be diagonally opposite the doors so you get airflow accross the room

our single big air handler is hung on threaded rods, and at full noise on the fan there is no vibration or noise in the (kids)bedroom that the unit sits above. the loudest noise is in the hall where the 2 large air return suctions are but thats not very loud. at no time is the aircon louder than rain on our tile roof. Infact the biggest source of noise is infact the robinhood rangehood which shakes the bajeezus out of the wall.

also what fan setting do you use? try using the eco setting so the unit isnt reacting as much.

we only have one thermostat for the whole house but i guess our installer did his job properly as the bedrooms are about 1-2 dgrees cooler than the lounge/living which is fine by us. using the adjustable vents for winter/summer would help too. we have the adjustable thermo vents

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