A question about : Air Source Heat Pumps/Air Con
With all the posts ongoing here regarding heat pumps etc I have decided to start a new post I have put together with information on reverse cycle air conditioning (heat pumps), where people can ask questions, chat about heat pumps, discuss experiences, installs, electricity usage & anything else heat pumps related.
Theres a lot of info here to take in, please do read it all as this may just
How does it work?
It's actually quite simple. Air conditioners work in much the same way as your refrigerator except there are two separate, but integral, parts to the system. There is an outside unit housing the compressor that is similar to the exterior back of your fridge. It draws warmth from the outside air in even the coldest of weather. That warmth is then transferred inside the home using a refrigerant process through a piping system powered by an indoor fan unit that is typically mounted to the wall. This is why the system is also often referred to as a heat pump rather then air conditioning. Both are in fact the same. Similarly, in summer, the reverse happens. Warm air is drawn from the interior room and expelled by the outside unit.
Heat Pumps are capable of transferring up to 4kW of heat into a space while only consuming 1kW of electrical energy. The energy efficiency of a heat pump will decreases as the temperature difference between inside and outside becomes greater, even at low temperatures a heat pump can provide 3 times as much heat as a normal electric space heater would provide with the same amount of electricity input. This makes Heat pumps extremely energy efficient.
Not all Heat Pumps are designed to continue working where temperatures fall below freezing point
The principle of air conditioning always comes down to the same:
absorb energy in one place and release it in another place
The process requires an indoor unit, an outdoor unit and copper piping to connect both. Through the piping the refrigerant flows from one unit to another. It is the refrigerant that absorbs the energy in one unit and releases it in the other. 
Cooling mode (Heating mode is the same but in reverse)
1 Indoor unit
A fan blows the hot indoor air over a heat exchanging coil through which cold refrigerant flows. The cold refrigerant absorbs the heat from the air and cooled air is blown into the room.
2 Copper piping
The refrigerant circulates through the units and the piping and takes the heat from the indoor unit to the outdoor unit.
3 Outdoor unit
Through compression, the refrigerant gas is heated and its boiling point increases. In the outdoor unit the obtained heat throught compression is released to the outdoor air by means of a fan which blows the outdoor air over a heat exchanging coil.
4 Refrigerant
The liquid refrigerant flows back to the indoor unit.
5 Indoor unit
Back in the indoor unit, the refrigerant is decompressed and thus enabled to extract heat form the indoor air.
Comparison of 2400w fan heater & Heat Pump Running Costs:
https://www.bdt.co.nz/comfortmaster/data/guides/WinterRunningCostsCompar... - this is for Mitsubishi Electric but savings made on other manufacters however these will vary.
Inverter Technology:
Here's some info about inverters, the same applies across all manufacturers however efficiency levels are different but the operation side of things is the same. There is an article at the bottom from Mitsubishi Electric where they have done a comparison test for a fan heater and heat pump. This is not unique to Mitsubishi Electric, similar costs will be seen across all heat pumps... its a very efficient technology. Different manufacturers will have different efficiencies. The best manufacturers are Mitsubishi Electric, Daikin, Mitsubishi Heavy Industries, Fujitsu, Sanyo, LG, any other manufactures are entry level and will not offer as good quality systems or efficiencies.
Inverter systems save energy by using a variable controlled Compressor. The output is controlled to only provide the energy required to keep the room to the set temperature. By reducing the output required less power is used and this substantially reduces power consumption. Inverter control not only saves you money but also keeps you more comfortable.
Inverter System or Fixed Speed System?
What is a Fixed Speed Split System?
This system only has a single speed compressor motor that is either on or off.
It works similar to a fan heater that switches off when the desired temperature is reached and on again when the temperature drops to a set level. It speeds up or slows down to calculate the heat loss from the space to be heated ensuring it is only putting in the same amount of heat that the space is losing.
What does Inverter Mean?
Inverter technology uses a variable speed compressor motor similar to a car. It simply slows down and speeds up as needed to hold a selected comfort setting.
Inverter technology provides a more precise room temperature without the temperature fluctuations of fixed speed systems.
Inverter vs Fixed Speed:
Inverter Systems are Approximately 30% more efficient than fixed speed systems.
Inverter systems reach desired room temperature quicker.
The speed control of the outdoor unit also means quieter operation, this is important especially at night in residential areas.
Inverter Systems
Increased output to achieve set temperature faster.
Then varies the output to maintain a constant room temperature.
Fixed Speed Type
Slowly gets to temperature as output rating is fixed.
Then turns on and off to maintain room temperature.
Sizing of units:
Read the following guide for sizing info: Excuse the references to Australia and New Zealand this contains useful info:
https://www.bdt.co.nz/comfortmaster/data/guides/heatpump_sizing_quidelin...
What type of unit is best suited for your property:
Heat Pumps / Air Conditioners are manufactured with various indoor unit options. High Wall Type, Ceiling Cassette Type, Floor Mounted Type, Concealed Ducted Type, and Under Ceiling Type.
High Wall-mounted
The most popular residential unit choice. These units tend to be the quietest as well as taking up no floor space.
Compact Floor Console
The floor mounted are more designed for heating applications. They are ideal for space heater or gas fire/fireplace replacement. They can be recess mounted into the wall cavity giving a shallow profile for hallway installation.
Ceiling Cassette
The ceiling mounted units take up no floor space. These units have four way air direction and have adjustable air flow patterns. These units are more suited to larger floor areas & commercial properties.
Ceiling Concealed (Ducted)
These units are mounted in the ceiling space and are unseen in the conditioned space. The only visible presence is the supply and return air grilles.
Ceiling Suspended
These units are more suited to high stud large room areas. They tend to have high airflows and are more suited to commercial applications.
Multi-Split Systems
Multiple Indoor Units can be Connected to a Single Outdoor
Connect from 2 to 8 Indoor Units
Many Combination Patterns to choose
Energy Saving and Quiet Operation
Five Multi-Split Systems from 6.4kW to 16.0kW (Heating)
Inverter Multi-Split system models are designed to allow several indoor units (regardless of capacity or type) to be connected to a single outdoor unit. This allows you to select the model best suited to each and every room in your property.
Example: 3x Bedrooms and 1x Office
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Location of units:
Indoors:
Don’t locate units with obstructions in front.
Result:
Short cycling of air back to units room sensor making the unit think its wamer/cooler than it actually is.
Air is not circulated correctly leaving cold/hot areas in room.
Try to locate the indoor unit where the airflow is pointing to the other areas of the house that may require residual heating/cooling.
Outdoors:
Avoid paved areas unless a drain kit is fitted. Result: Units condensate and drip water. May cause slime build up or ice. If no other place please advise customer.
Noise:
Outdoor inverter units are very quiet and have scroll compressors, watch the following video and you will see mine in action:
https://www.youtube.com/watch?v=-mUzYHEfQEY
Defrost Cycles & Correct Sizing of Outdoor Unit:
Defrost will happen in all climates, however the lower the humidity the less frequent it will defrost as it takes longer for it to build up on the outdoor coil.
You will probably not even notice it defrosting, if you buy a decent brand system you will find that the defrost strategy is very good so that it doesn’t take long to defrost.
When they defrost you will find that the system goes into reverse, taking heat from the inside circuit to the outdoor unit so it defrosts. This will last about 5 minutes depending on how much ice has built up but you have to look at the unit to notice it doing it as it doesn’t start making things cold inside. The unit just doesn’t heat during that time.
Some units in New Zealand or other countries that have very cold winters have units optimised for that country, i.e. defrost cycles instead of stopping and going into reverse will inject hot gas into the outdoor unit whilst the unit is heating so that it doesn’t actually stop heating. Currently can only find info on Sanyo air to air heat pumps in this country that do this... not sure of a system that does this on a unit that will provide this on hot water but you can see the technology is there. As I say you don’t need it in the UK climate our winters are not as harsh as some countries.
The best method for new builds is under floor heating, nice even temps throughout, however longer warm up times due to the lower water temperature but if left on during cold weather you will be fine.
I personally prefer fan coil units as these double up as cooling/ac for the summer and provide very fast warm up times.
Most air to water outdoor units can be used with fan coil units... you just use a fan coil instead of a water coil in the floor.
Mounting of unit... must be installed in the open, no enclosure, so no garages, lofts or corners the unit must be in the open air.
A user in another post:
https://forums.moneysavingexpert.com/showthread.html?p=29040015#post2904...
He installed it in the loft and it froze the loft in the cold weather and thawed and caused leaks into the house below, this happened twice and after this he decided to mount the unit outside and it performed better as it was effectively turning the loft into a giant fridge/freezer.
Here’s some more info on heat pumps:
Defrost Strategy
When the outside temperature drops below zero all heat pumps must perform a “defrost cycle” to remove ice build up on their outdoor coils.
Defrost strategy is determined by individual Heat Pump manufacturers. These strategies vary greatly between brands. Older style Heat Pumps initiated defrost by a fixed time or coil temperature. This system was not efficient as it often caused Heat Pumps to defrost too often or effected performance by not defrosting often enough. Defrost cycle is required when the outdoor coil is too cold or covered in ice preventing heat transfer and unit performance.
All Heat Pumps must defrost. heats pumps utilise a Fuzzy Logic software program, a form of Artificial Intelligence contained in the chip of the outdoor unit and typically lasts between 3 to 5 minutes.
The program measures and records:
- Ambient Temperature
- Outdoor Coil Temperature
- Accumulated Continuous Heating Running Times
- Defrost Initiation Time and Termination Times
The program optimises this data based on history to produce defrost initiation only when absolutely required.
This is important as Heat Pumps are unable to produce heat when they are in defrost mode. This is extremely important to real performance in low ambient conditions.
Defrost Cycle Management
Heat Pumps optimise its defrost cycle once selected in three ways:
When the outside temperature drops below zero all heat pumps must perform a “defrost cycle” to remove ice build up on their outdoor coils.
Defrost strategy is determined by individual Heat Pump manufacturers. These strategies vary greatly between brands. Older style Heat Pumps initiated defrost by a fixed time or coil temperature. This system was not efficient as it often caused Heat Pumps to defrost too often or effected performance by not defrosting often enough. Defrost cycle is required when the outdoor coil is too cold or covered in ice preventing heat transfer and unit performance.
The program measures and records:
- Ambient Temperature
- Outdoor Coil Temperature
- Accumulated Continuous Heating Running Times
- Defrost Initiation Time and Termination Times
The program optimises this data based on history to produce defrost initiation only when absolutely required.
This is important as Heat Pumps are unable to produce heat when they are in defrost mode. This is extremely important to real performance in low ambient conditions.
1. Compressor Control
When a Heat Pump is defrosting it is not providing heat to the controlled space. It runs the compressor(inverter drive) at maximum speed during defrost to bring the outdoor coil up to temperature as quickly as possible. This melts any ice formed on the coil fins quickly and minimises defrost time. Minimising defrost time maximises heat output per hour real time.
2. Dry Coil Defrost Cycle
Once the outdoor coil is up to temperature and the compressor cycle has completed there is generally water between the outside coil fins. If the outdoor unit were to immediately resume heating the outdoor coil would freeze and prevent heat exchange. To prevent this the outdoor fan is run at maximum speed prior to resumption of the heating cycle. This is often characterized by steam blowing from the outdoor unit. This ensures the coil is completely dry before the heating cycle resumes.
3. Time optimization through Fuzzy Logic
Time between defrost cycles is continually being reviewed and optimized by the Heat Pump microprocessor software. Algorithmic calculations based on previous history is used to calculate the next defrost period.
Fuzzy Logic or learning logic is a form of artificial intelligence. Defrost cycle termination is based on a combination of time and temperature. These parameters are used to calculate the next defrost period.
Outdoor Humidity
Outdoor humidity also effects heating performance. Areas that have a “dry cold” or low humidity such as “Mount Cook” will perform better at low ambient than say Taupo where ambient conditions can reach zero and “misty” moisture laden air conditions exists. The more moisture in the air the more moisture will freeze on the outdoor coil.
Incorrect Unit Selection
If a unit is selected that is too small the Heat Pump will run continuously and never reach set point. This continuous running will increase defrost requirements by reducing the outdoor coil running temperature and driving it into sub zero temperatures for excessive periods. The unit will defrost at the minimum intervals and may never catch up and achieve set point.
Location of Outdoor Unit
Location of the outdoor unit is essential for low ambient performance. Units located under houses, decking and in areas where airflow is impeded may create their own microclimate (i.e. giant fridge/freezer or in summer oven) and reduce the effective outdoor ambient temperature that the units operates in. Locating the outdoor unit too close to a wall and not observing clearances will also prevent the unit from delivering full output.
Get the correct sized unit:
Choosing the right sized Heat Pump is key to ensuring optimum comfort levels. Every home is as individual as its owner. The key to selecting the right Heat Pump for heating your home is choosing the correct unit size. Choosing the wrong size can cost you more in power consumption.
Insulation and building orientation are key aspects in terms of potential heat loss a home is effected by. An older style home with poor insulation will lose indoor heat much quicker than a modern well insulated home that faces north.
The quicker a home loses its heat, the bigger the Heat Pump system will need to overcome this heat loss.
Best answers:
- Manufacturer Websites & Further Info:
https://www.bdt.co.nz/smarterheating/home.aspx : Contains all the info above plus lots more including sizing guide & running costs calculator on heat pumps... very useful however its an Australian site.
https://www.mitsubishi-aircon.co.uk/ : Mitsubishi Electric UK Website -
https://www.mhi.co.jp/en/aircon/index.html : Mitsubishi Heavy Industries Website
www.daikin.co.uk: Daikin UK Website
www.sanyoaircon.com : Sanyo Website
https://www.fujitsu-general.co.uk/aircon/index.htm : Fujitsu Website
https://uk.lge.com/products/category/list/airconditioning.jhtml : LG UK Website
If you feel I have missed something out then let me know and I will add it to the main post.
Mods it would be good if you can have this as a sticky topic so we can avoid duplicates and have all the info in one place.
Air to Water Systems:
Some users are looking to replace traditional gas heating & hot water for heat pumps:
Heres some info on how this works:
Many manufactures listed above are offering similar systems, so shop around to get the best prices, again however the efficiencies and capacities will differ.
Here are 3 of the best systems:
https://www.altherma.co.uk/for_the_home/default.jsp- Daikins Altherma
https://www.altherma.co.uk/default.jspMitsubishi Electrics Ecodan
https://www.mylg.co.uk/data%20for%20s...%28AWHP%29.pdf - LG's Therma V - Here are the developments made 2000 - 2007 to ASHP's which have resulted in a constantly improving performance:
(1) Compressor
a) High-efficient compression technology
The Compressor is the heart of an air conditioner and requires high-precision
processing technology.
Although a rotary compressor with rotary method was widely adopted before, a
twin rotary method or scroll method with better compression efficiency has now been
developed and adopted.
(2) Fan
a) Indoor Fan
Various types of fans are used for indoor units depending on unit form. A "cross
flow fan" is used for most of the wall-hung type air conditioners.
Although a cross flow fan was composed of blades that were processed metal
sheets in the past, an attempt to increase air volume has been made through
introduction of plastic blades having a wing-shaped section and growing size of fan
diameter, while controlling noise.
The layout and molding of a fan and blades have also been improved, by having
random spacing between blades, angling a fan shaft, etc.
b) Outdoor Fan
In general, a propeller fan is used for an outdoor unit of an air conditioner.
Although it was made of processed metal sheets in the past, it is now made of plastics.
An attempt to increase air volume has been made by improving a blade shape, while
reducing noise.
c) Fan motor
For fan motors for both indoor and outdoor units, an efficient DC brushless
motor has replaced a conventional AC motor.
(3) Electronically controlled expansion valve
A decompressor is a component to create high-pressure and low-pressure states in
a refrigerant circuit. Until now a capillary tube has been used primarily. A capillary
tube refers to a thin and long copper pipe being about 0.2 to 2 m long and having an
inside diameter of 1 mm to 2mm. This pipe generates pipe resistance and achieves
throttling action (decompression).
A capillary tube has been widely used for a room-air conditioner as it can be
implemented with a simple structure. However, adjustment of appropriate degree of
throttling according to number of revolutions is not possible because the degree of
throttling is constant even when the number of revolutions of a compressor varies.
Thus, an electronically controlled expansion valve has become used, which
enables appropriate degree of throttling based on an electronic signal from a
microcomputer determining the operating state of an air conditioner. The valve is
structured so that a pulse motor rotates based on an electronic signal, and a gap
between the valve and the valve seat is adjusted by converting the rotation into
up-and-down motion, thereby controlling the degree of throttling.
This could achieve efficient control of refrigerant flow, depending on the operating
state, such as changes in number of revolutions of a compressor used in an inverter air
conditioner. Thus, the electronically controlled expansion valve has become mainly
used.
Heat exchanger
A heat exchanger is one of the important components of an air conditioner. It
exchanges heat between indoor air and refrigerant in an indoor unit, and between
outdoor air and a refrigerant in an outdoor unit.
A fin-tube-type heat exchanger, in which a copper tube for refrigerant penetrates
a plate-form aluminum fin for air, is used for this heat exchange.
Shape of heat exchanger
In separate wall-hung type indoor units that account for most of the room-air
conditioners, a cross section of the conventional heat exchanger was molded like a
plate. However, in order to expand heat exchange area in a limited space, those of
bent type and those molded in a curved surface have been developed.
In addition, heat exchangers in an initial indoor unit were arranged in two
columns. However, improvement has been on the way to increase the heat
transmission area and to augment the heat exchange capacity by means of partially
arranging them in three columns, as long as an indoor unit structure can afford
enough space for it. - A lot of people are asking in the forums how noisy the units are:
The indoor unit is very quiet, quieter than a desk fan.
The outdoor unit noise has been captured in this video the best it can. Its in heat mode as this is when the outdoor unit has to work its hardest. In cooling mode the fan rotates much slower and the noise in general is hardly noticeable, I think you will agree in heating mode it is also very quiet...
https://www.youtube.com/watch?v=-mUzY...e=channel_page - The unit we've had in the conservatory for 18 months has completely conked & have been told we need a new unit.
Any opinions on Samsung units?
Thanks - i have a biggish old house with poor insulation and limited cost effective opportunities to improve this.
Does this mean ASHP are not for me ??
:confused: - had ancient gas boiler that was condemed a while back (lovely cold winter living out of one room)so looking to replace/ install whole new system. have been advised that all plumbing will need replacement for a new gas boiler.
looking at multi fuel with back boiler;, ASHP and any other innovative ideas for long term future proof option. no intention of moving for many years so will spend some but as always cash is tight
cheers - I've read this thread and others with great interest as I'm looking to install something like the Mitsubishi Heavy Industries SRK25-ZGX Air Con unit primarily for heating. They seem to give a much higher COP than most others. My preferred installer likes Daikin but these are all around 3.5 COP versus Mitsubishi's 5 though all are A/A energy rated.
What I'm trying to find out is whether the Mitsubishi really does deliver a COP of 5, how that changes with loading (if at all) and how the COP falls as o/s temperature drops to around freezing. Or is this the A/C world's equivalent of the car fuel consumption figures? - The cop will fall as temperature drops below 5C but at -15C the unit will stll have 85% capacity in most instances. The cop is based on normal uk temps. MHI are not the same company as MITSUBISHI ElECTRIC. Both are different products with diff spec so make sure you are researching the right brand!
Cop is much talked about on the heat pump posts. The most important part is how much capacity you have in the unit at -15C, cops of around 3.5 are good and the figure of 85% capacity is good at -15C. At -5C your still going to have full capacity. They are rated down to -15C and how often does it get to that in england during the day or evening?
Daikin is excellent, mitsubishi electric is excellent, MHI is also good but Mitsubishi Electric comes before MHI or Daikin on the COP figures and efficiency. - As pointed out previously Cardew, the house has no insulation, we have 12ft high ceilings and an open cellar beneath the floors. Thick solid walls and no insulation at all in the walls or the floors, or the attic. Its a victorian house built in 1900 The house can drop to about 8c in about 5 hours if its been very cold. The central heating in winter is set on 80C and the radiators are large double ones and correctly sized.
We have doulbe glazing but it is very draughty. As its a rented flat theres not much I can do about it! - Hi Richard!
I posted in the other A/C thread that I have been using my Fujitsu heat pump system to warm the house this Winter after my boiler failed.
Well...I took the plunge and replaced the old gas boiler - with an Air to Water Heat Pump!
Best investment ever! It is only a 5KW pump, but is maintaining the temperatures in my 2 bed bungalow with no problems at all. I leave it running 24/7 and let it do it's thing. It is costing Ј1.50 - Ј2 a day to run which compares very favourably (cheaper to run!) with my Gas bills of approx Ј200 a Quarter. And I now have heat and hot water 24/7 which suits my chaotic (due to work) lifestyle.
The unit is one of the cheaper ones - a Trianco, Activair and it's in the loft! It is only just audible is you stand beneath where it is mounted (above the bathroom).
I plumbed it so that it heats the hot water tank as priority, then the return continues around the heating system before going back to the unit for reheating.
The hot water tank is always hot and each room has it's own thermostatic valve.
Living room set at 22C
Master bedroom 21C
Second bedroom 18C (not currently in use)
Kitchen 21C
Hallway 20C
Bathroom 23C
The unit cost Ј925 which is comparable to a boiler, but I now don't have servicing costs, didn't have to pay a CORGI engineer to fit it and will benefit from much lower bills going forward. - Hi Andy, who advised putting it in the loft?, how did you drain the condense? and when it has pulled all the heat from your loft, how does it perform?
- Andy very good what you have done but all manufacters i know advise the outdoor unit to be installed in open air. For instance most peoples lofts are not big enough to have a unit installed in them. Lofts are draughty but they are not fully open to the outside air. YOu say your loft is always warmer than outside thats crazy... (not that i dont believe you) but I have heard customers have had those self install units and put them in the loft. In heating the loft starts of at 5C but then quickly after about an hour the loft is at -10C and the unit is unable to remove any more heat and over working.
Lofts are ventilated but not enough airflow for a unit. However you must have a large loft if you have proved the air temp doesnt drop. You may find yoou have to clean your coil more as dust in lofts is quite fine and may clog the coils.
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