Daikin Altherma - Defrost Cycles to frequent

[src100308]

I have recently had a High Temperature 16KW Daikin Altherma installed. The unit seems to work fine at outside temperatures above 5 degrees heating the house to 18 degrees without issue.

However as soon as the the temperature drops defrost cycles increase in frequency. At minus 2 degrees the unit goes into defrost every 30 to 35 minutes.

Is this normal? This frequency of defrost is resulting in it not maintaining an internal temp of 18?

thanks for any advice or help

[Bigfreeze]

I have recently had a High Temperature 16KW Daikin Altherma installed. The unit seems to work fine at outside temperatures above 5 degrees heating the house to 18 degrees without issue.

However as soon as the the temperature drops defrost cycles increase in frequency. At minus 2 degrees the unit goes into defrost every 30 to 35 minutes.

Is this normal? This frequency of defrost is resulting in it not maintaining an internal temp of 18?

thanks for any advice or help

Here we go again Lads

Have a look through the other Altherma threads here and you'll see a similar trend

(BTW i'm not dismissing your thread, we just see this problem so often round here. Though some argue its just not true)

[Brian_UK]

If it has only recently been installed contact your installer immediately and complain.

Get them to confirm the load calculations and design data.

[src100308]

Thanks for the replies - I have been back to my installers and they have advised that this is normal function at low temperatures. I'm looking for a second opinion - any advice much appreciated!

I've searched the forums for others with a similar issues. Any chance you could point us in the right direction.

tks again

[mad fridgie]

Thanks for the replies - I have been back to my installers and they have advised that this is normal function at low temperatures. I'm looking for a second opinion - any advice much appreciated!

I've searched the forums for others with a similar issues. Any chance you could point us in the right direction.

tks again

Your installers are correct the defrost is a normal function.
What are you heating with the water, rads, underfloor?
Are you using a timer to turn the system on and off?

[src100308]

its switched on an off by a room thermostat which is set to hold the indoor temp at 18 night and day. The unit is heating new installed radiators which collectivley add up to about 16kw. The rads are oversized by roughly 50%.

[Bigfreeze]

its switched on an off by a room thermostat which is set to hold the indoor temp at 18 night and day. The unit is heating new installed radiators which collectivley add up to about 16kw. The rads are oversized by roughly 50%.

These units defrost regularly (esp in the -2 to +7 range) because of the very tight fin spacing utilised in the units. They extract alot of energy from a very small package, the downside being the overly frequent defrosts. The units are operating as normal. Its a characteristic of these units that you'll just have to live with.

If you look down through the history of my posts you'll see I referred to this issue on numerous occasions and that will lead you to the other threads I mentioned.

[mad fridgie]

its switched on an off by a room thermostat which is set to hold the indoor temp at 18 night and day. The unit is heating new installed radiators which collectivley add up to about 16kw. The rads are oversized by roughly 50%.

Would it be fair to say that you had your heat load calculated to 16Kw?

[sinewave]

Got a 16kW HT unit in our house.

Yes they do cycle on to defrost a lot in minus ambients but ours maintained a 21-22 degree setpoint even in the recent -12 degree C cold snaps.

I have found through trial & error that taking the unit off the auto setting (Weather dependent setpoint) and selecting a manual water leaving setpoint of 65 degrees C works far better.

We also have three programable room stats (3 storey house) which work better than using the inbuilt stat in the Daikin controller.


As an aside I hope your outdoor unit is not floor mounted?

Daikin UK have agreed to replace quite a few outdoor coil assemblies I'm told due to them bursting with massive Ice build up in these recent cold ambients.

They have now altered their install instructions to stipulate that outdoor units need to be a minimum of 300mm of the deck!

[frank]

We also have three programable room stats (3 storey house) which work better than using the inbuilt stat in the Daikin controller.

I may have mentioned, but can't recall, that with the multi point pcb you can have 2 set points for the water temperature.

So, if you wanted to have your bedrooms with a lower flow temp, you could wire the remote stat for that floor to the second set of terminals on the pcb and programme the controller accordingly. When only that floor calls, the water temp is lowered automatically - can be handy at night

[jimmy wilkes]

any other people out there with good tips on altherm?would gud to hear them please.have installed about 20 split types&2 monoblocks.would be intersting to see how you guys are setting systems up.how are engineers setting up when the client has 2 pumps for underfloor systems aswell as hydrobox pump?

[Mabe]

Defrost every 30-35 minutes?? it's to much in normal conditions but it can happen if the unit is not installed high enough and ice is build up. when this happen the evaperation sensor is quick minus 10 degrees and together with cold ambient temperature altherma goes into defrost.

[sinewave]

As you can see from these pics my unit does create a lot of Ice (pic 1 shows a 5" thick 'Ice Rink' below the unit) but the coil defrosts OK and does not impair heating performance too much in ambients of -12C or less.

[desA]

Heated under-trays & drain pipes will be next.

Going 'green' has its challenges.

[frank]

Taken from the Altherma HT Service Manual (Draft)

Defrosting Operation
The defrost operation is performed to solve frost on the outdoor unit heat exchanger when
heating, and the heating capacity is recovered.
[Conditions to start]
The defrost operation is started referring following conditions.
• Outdoor heat exchanger heat transfer co-efficiency
• Temperature of heat-exchange (Tb) < Tdef*
• Timer (25 min. the minimum)
In addition, outdoor heat-exchange co-efficiency is derived from Tc, Te, and the compressor
load.
*Tdef can vary but is at least -10°C
[Fan defrosting]
• When compressor stops, 80 sec. at low RPM
• At start up compressor, 30 sec. at 950 RPM
• Then goes back to normal RPM

[frank]

Just found the Defrost Strategy for the Altherma LT version

[src100308]

tks for the replies to these threads - really useful. There is no build up of ice on the outdoor unit and yet there is a defrost every 45 ish minutes with an outside temp of 5 degrees. Only just maintaining an indoor temp of 18 - I think the issue is the rads don't have the chance to get anywhere near a decent temp - at most 55 degrees.

Are there any settings that can be checked to see if the defrost settings are configured correctly?

I notice in the defrost strategy that heating load is a factor when the unit decides whether or not to go into defrost. Does this therefore mean that significant improvements to insulation/pipe lagging will reduce the frequency of defrosts

[Bigfreeze]

tks for the replies to these threads - really useful. There is no build up of ice on the outdoor unit and yet there is a defrost every 45 ish minutes with an outside temp of 5 degrees. Only just maintaining an indoor temp of 18 - I think the issue is the rads don't have the chance to get anywhere near a decent temp - at most 55 degrees.

Are there any settings that can be checked to see if the defrost settings are configured correctly?

I notice in the defrost strategy that heating load is a factor when the unit decides whether or not to go into defrost. Does this therefore mean that significant improvements to insulation/pipe lagging will reduce the frequency of defrosts

You need to oversize your rads. 55C is too high for a heatpump. Your COP is shot and you're running at very high head pressures constantly which will shorten the life of the equipment.
You should really install fan assisted convector rads and also a buffer tank to ensure you have enough water circulating through the heatpump on defrost. You would be better off running oil if you continue to run at these temps

[src100308]

Rads are already oversized by about 50% and the heat pump is a 16kw high temperature unit meant to be capable of 80 degrees. Is 55 degrees still an unfair ask?

[Bigfreeze]

Rads are already oversized by about 50% and the heat pump is a 16kw high temperature unit meant to be capable of 80 degrees. Is 55 degrees still an unfair ask?

For every degree you rise in temperature you drop 2% efficiency. The european standard for ASHP's is an Air temp of two and a water outlet of 35. The Daikin units are rated at a COP of 4.
You are going 20 degrees above the rated temp so your efficiency is dropping 40%. For every degree you go below an air temp of 2 you lose 3% efficiency. Lets say the temp is -5. That means a further 21% efficiency drop.
So as you can see your COP is down 61% so it is now a COP of 1.56. So inreality what you have is a glorified immersion/resistance heater. It would be far cheaper to heat the house on oil at those figures. You heat output is also dropping as temperature drops.
In order to make this work you really need to get the way you distribute the heat work with a water temp of a maximum of 40C. The lower the better though.

You should consider something like these..
http://www.dimplexrenewables.com/brand/DIMPLEX-SMARTRAD

[wozza]

For every degree you rise in temperature you drop 2% efficiency. The european standard for ASHP's is an Air temp of two and a water outlet of 35. The Daikin units are rated at a COP of 4.
You are going 20 degrees above the rated temp so your efficiency is dropping 40%. For every degree you go below an air temp of 2 you lose 3% efficiency. Lets say the temp is -5. That means a further 21% efficiency drop.
So as you can see your COP is down 61% so it is now a COP of 1.56. So inreality what you have is a glorified immersion/resistance heater. It would be far cheaper to heat the house on oil at those figures. You heat output is also dropping as temperature drops.
In order to make this work you really need to get the way you distribute the heat work with a water temp of a maximum of 40C. The lower the better though.

You should consider something like these..
http://www.dimplexrenewables.com/brand/DIMPLEX-SMARTRAD

Big Freeze, Dont agree with you on this one.
The system he is talking about is a High Temperature system and has a better efficiency at 65degrees flow temp as it is a cascade system.
If it was a low temperature system i would agree.

I would definately check the load calcs, if they have said the heat loss is 16KW, at lower temperatures the capacity of the unit drops ( as with any heat pump) resulting it working harder= more frequent defrosts.

[Bigfreeze]

Big Freeze, Dont agree with you on this one.
The system he is talking about is a High Temperature system and has a better efficiency at 65degrees flow temp as it is a cascade system.
If it was a low temperature system i would agree.

I would definately check the load calcs, if they have said the heat loss is 16KW, at lower temperatures the capacity of the unit drops ( as with any heat pump) resulting it working harder= more frequent defrosts.

Wozza I checked out the specs on the high temp system. At 55 it says has a COP of 2.57 but thats at an air on temp of 7 so I don't think I'm that far out. it may well be a cascade system but more energy is required to get to that temp regardless. The 16kw is also rated at 7C which I feel is very misleading as it is not the european standard

[mad fridgie]

Here is a simple example how temperature of water effects performance of a heat pump/refrigeration system
Based upon 10C difference in water temp (all things being equal)
Example Copeland R410a
40SCT HOR(heating) 12.1Kw power draw 3Kw (COP 4.03)
50SCT HOR 11.5kw power draw 3.9Kw (COP 2.95)
Lets say a heating season of 100days and a daily heating load of 180Kwhrs
40SCT= Run hours 1488, power drawn = 4464kwhrs
50SCT= Run Hours 1565, power drawn = 6104kwhrs
Difference= 1640.
Adds up and you would be more cosy (with big rads)

[back2space]

You should consider something like these..
http://www.dimplexrenewables.com/brand/DIMPLEX-SMARTRAD

They look fantastic I bet the price tag is high though!

[Bigfreeze]

They look fantastic I bet the price tag is high though!

Between €300 and €400 depending on output. They do work well though. Only way to go if you must use rads. Those or solo convectors but I heard the solos can be a little noisy

[back2space]

Between €300 and €400 depending on output. They do work well though. Only way to go if you must use rads. Those or solo convectors but I heard the solos can be a little noisy

In effect a glorified indoor a/c unit I don't know why they are so expensive. You can buy a 3.5kw indoor unit for an ac for less than that.

They should charge less they might sell more. Can u imagine the cost of one of these for every room.

[Bigfreeze]

In effect a glorified indoor a/c unit I don't know why they are so expensive. You can buy a 3.5kw indoor unit for an ac for less than that.

They should charge less they might sell more. Can u imagine the cost of one of these for every room.

I know, I've had to quote for them once or twice and they were always a non runner because of cost. They're just a fin coil with a cylinder fan and a little stat. If they sold them at €150 - €200 they'd probably sell 5 times what they currently do.

[MikeHolm]

BF, are used old style cast iron not available where you are? I get so pissed off when renovators rip them out here and put them in the scrap. They would work fine for many of these situations when you cannot have floor heating.

[Bigfreeze]

They are Mike, but you'd want your communion money with you if you went to buy some, they're a horrendous price

[MikeHolm]

Whereas the used ones here are about $5-6/section. I can get 1kw @ 40C for $70-80. The supply is slowly decreasing as many renovators smash them up.

[MikeHolm]

Time for me to get an old barn in the country and start hoarding

[brunstar]

For every degree you rise in temperature you drop 2% efficiency. The european standard for ASHP's is an Air temp of two and a water outlet of 35. The Daikin units are rated at a COP of 4.
You are going 20 degrees above the rated temp so your efficiency is dropping 40%. For every degree you go below an air temp of 2 you lose 3% efficiency. Lets say the temp is -5. That means a further 21% efficiency drop.
So as you can see your COP is down 61% so it is now a COP of 1.56. So inreality what you have is a glorified immersion/resistance heater. It would be far cheaper to heat the house on oil at those figures. You heat output is also dropping as temperature drops.
In order to make this work you really need to get the way you distribute the heat work with a water temp of a maximum of 40C. The lower the better though.

You should consider something like these..
http://www.dimplexrenewables.com/brand/DIMPLEX-SMARTRAD

Wozza I checked out the specs on the high temp system. At 55 it says has a COP of 2.57 but thats at an air on temp of 7 so I don't think I'm that far out. it may well be a cascade system but more energy is required to get to that temp regardless. The 16kw is also rated at 7C which I feel is very misleading as it is not the european standard

Hi Big freeze,
I don't agree either, the reason for that is that there are 2 conditions that the units are tested under if you have a look at the technical data.
The other thing is that using 2 compression cycles you run two compression cycles with lower head pressure.
2 refrigeration cycles with lower head pressure.
The best COP values on the high temperature systems will be at 65 degree flow. With any refrigeration cycle, lower the condensing pressure and temperature and it will become more efficient.

[src100308]

hi, still having issues with my altherma - it works well until outdoor temp drops to two degrees and then the regular defrosts start approx every thirty minutes. Defrosts this regular mean that its not heating long enough to get to its target flo temp of fifties and not long enough to heat the house sufficiently.

Does anyone know if there is a field setting to alter the defrost strategy. Looking at the outdoor unit there is no indication it needs to defrost as regular as it does.

[brunstar]

What is the size of your property and how many radiators /underfloor loops do you have connected to it?
Poor flow rates through your indoor unit can also cause this.
What is the length of pipe between the indoor unit and outdoor unit?
If the system is sized incorrectly this can occur.
What temperature is the system designed to operate to?
If the system is sized correctly and the flow temperature never rises above 55 degrees then there could be non condensables within the refrigeration circuit.
Have you contacted your installer?

[src100308]

Tks for reply brunstar, The property is 200msq the distance between the indoor and outdoor is approximatley 18m. There are 15 radiators attached and the system is designed to operate up to 80 degrees (its the HT model) but really just to 65 degrees. In outdoor temperatures of above 3 degrees the unit will climb to a flow temperature well into the sixties - i.e. it doesn't defrost half as often. The system works as you would expect it to above outside temps of 3 degrees.

It is a 16kw unit and the overall heat demand for the property has been calculated to 16kw. Tks

[brunstar]

A good reply.
As you can see the heat loss is calculated at 16kw, this heat pump will give you about 16kw at 7 degrees, at -2 you will have an output from the heat pump at 13kw or so, during the colder spells it would be best to leave the system running 24 hours a day to keep up with the demand as it may be a little short on capacity at the lower ambient temperatures.
Check with your installer that 580 grams of refrigerant has been added as this unit is only pre charged to 10 meters so if the pipe run is 18 meters and they have not added additional gas then this could also be a sign of what you are experiencing.