Air source heat pumps

[marc5180]

I'm hearing more and more about air source heat pumps and air to water heat pumps and i don't really know anything about them.

I think eventually the company i work for is going to be getting involved with them at some point so i'd like to understand a bit more about them, then
when i do eventually work on them, at least i will have a little bit of knowledge.

I have been looking on the net and have seen the Altherma and the Ecodan air source heat pumps.
As i understand these have are used for hot water and space heating and cooling?? and even under floor heating.

What about the air to water heat pumps, what are these used for and how do they work.

[mad fridgie]

This is a very wide feild,
The differences are really required outlet water temps and sanitory or not.
In practical terms heating water to upto 50C is not to hard and is has good performance, over this 50C is when things become more complicated.
For sanitry water depending upon where you live you need some for of double barrier, which in itself increases the SCT required (either via a direct heat exchanger or a secondary water loop)
The big argument sort lies in inverter or not, for me thers is no need as you are generally working large thermal mass and slow reaction times, so simple on/off controls are all that are required.
You will find that Many companies are moving into this market, (with varing methods)
As far as base components and principles no different to any other piece of refrigeration equipment.
I see the short to medium term problems being mis application and over selling the performance (both COP and heating output) We had this problem in NZ many years ago with air to air heat pumps, on cold days no where near enough heat (sales sized heating on nominal rating not real rating)

[desA]

Heat-pumps are a fascinating technology to get into. The problem is that many manufacturers continue to think of heat-pumps as a reverse air-conditioner & so consider it a simple technology to develop.

In reality, heat-pumps are very complex pieces of technology, operating at the very limits of known compressor operating envelopes. The components have to be precisely matched, if decent performance is to be obtained in the post 50'C heating range. Refrigerant charge is critical in these machines. Very few system components are rated at the temperatures at which heat-pump circuits operate - this brings difficulty for the designer.

The current flood of new entrants into the heat-pump market is sure to bring about a number of technology disasters, much like seemed to occur earlier on in the life-cycle of heat-pump technology (20-30 years ago). Compressors are what they are & if not managed correctly, will fail. This is the current Achilles heel of heat-pump technology.

The next difficulty lies in bringing a product to market at an affordable price - comparable to existing heat-generator technologies. This is no easy task, due to the complexities of heat-pump systems.

[Thermatech]

Some domestic AWHP are basically a split system outdoor unit with a refrigerant to water heat exchanger instead of an indoor unit.
Operating pressure, SH, SC, defrost its all the same stuf just different application.
The electronics & controls are a bit different.
So as an air conditioning engineer with lots of experiance working with split & VRF system you should find working with AWHP straight forward.

The high temp AWHP with cascade system are more complicated & for these some additional manufacturer training might be a good idea.

Ofcourse the water side is another matter unless you are trained experianced heating engineer.

My experiance over the last few years with water cooled VRF & AWHP is that getting the correct water flow rate is important. In some cases the water pump has been undersized & then in heating mode the unit is tripping on low water temp / frost prevention. This seems to be the most common problem I have been having with commissioning & trouble shooting.
Also air in the water system, pump switched off but no pump interlock with the HP unit, water volume flow rate too small, incorrect design of water circuit are all problems for the plumber / heating engineer to get right.

[mad fridgie]

Thermatech, is so correct, when it comes to heating systems (mainly underfloor in NZ) Flow Flow and Flow
Remember that in simple terms it is the SCT determine power consumbtion,

[desA]

Some domestic AWHP are basically a split system outdoor unit with a refrigerant to water heat exchanger instead of an indoor unit.
Operating pressure, SH, SC, defrost its all the same stuf just different application.
The electronics & controls are a bit different.
So as an air conditioning engineer with lots of experiance working with split & VRF system you should find working with AWHP straight forward.


I would differ completely from this point of view.

Heat-pumps optimisation & operation requires a different design emphasis to basic a/c. For AWHP, the evap sits in an uncontrolled space - this brings its fair share of problems - especially in hot, humid climates.

The temp lift of the typical water heating cycle forces the system to move across a vast range of thermodynamic points - some stable, others not. The system is in a continual state of flux - it is not a simple steady-state device.

Management of the system, correct charge fill & maintenance are critical.

As a simple quiz : How many peaks exist in a typical air-to-water heat-delivery curve over the complete temp lift range? Why?

[Thermatech]

Mark is a service engineer
I am also a service engineer.
We commission & trouble shoot mainly mass produced ac heat pump products.

So the product is already designed.

DesA is I think design engineer who does R&D with heat pumps so DesA has completely different view point.

However its always good to consider the design issues even if you never actually design systems yourself because it gives you much better overall understanding & as engineers we always tend to want to understand exactly how something works & why it works the way it does even if we only ever fix them when they go wrong.

BTW
A standard split ac system heat pump or VRF system can have to heat an indoor space from just arround zero to 25 deg C.
& thats why on Monday 4th Jan every ac contractor in the UK will have many calls from endusers who have found poor heating at there place of work as the heatpumps ac systems have a problem warming up a cold building that has not been occupied over the holiday period.

[chemi-cool]

How do you fight the problem of scale in the system?
Are there HE in a closed loop or the in coming water are new at all times?

Over here we use mainly the sun power with electric assistance and the heating elements have to be changed every few years because of the scale.

[desA]

DesA is I think design engineer who does R&D with heat pumps so DesA has completely different view point.

True... :D


BTW
A standard split ac system heat pump or VRF system can have to heat an indoor space from just arround zero to 25 deg C.
& thats why on Monday 4th Jan every ac contractor in the UK will have many calls from endusers who have found poor heating at there place of work as the heatpumps ac systems have a problem warming up a cold building that has not been occupied over the holiday period.

An interesting thought. I hope you get paid well for your efforts... ;)

[digerious]

danfoss go in to alot of detail about their products on their site and air source heat pumps are no exception.
everything from basic operation to wiring diagrams and technical info. you might find it helpful.

[cadwaladr]

one of my friends full time jobs is drawing up building plans,new builds etc,he was asking me about these pieces of kit,he is involved with the building of a new property which is going to have this type of equipment lalinstalled,the cost of getting three phase to the property was expensive,its seven bedroom a large house,but there is no secondary source of heating being fitted,big mistake i think,well we will see

[desA]

^ You may want your friend to think about ground-source heat-pumps for the base load part of his heating-load, with some AWHP's for make-up, when ambient temps are reasonable.

[Glades]

Heat pumps are an exact science.

If you're just getting into heatpumps...Read, read, read, and follow every bit of instruction...Try to convince the manager/owner to install quality units, matched sets, use a good sheetmetal guy you can count on and will learn with you, and that you cant be rushed for a fine finished product. get a monometre to span the entire lenth of your air handler...as air flow is King in heat pumps. That is if your refrigerant charge is precise.........Measure and adjust your airflow, super heat, subcooling all together to make a fine beast.

Every little bit is interwoven to make a long lasting efficient heating (and cooling) system.

In the pacific north west...(Vancouver Island) a customer who paid $10,000 for a new heatpump system would expext to have the unit paid off with energy savings in about 7-8 years...not bad!!!

[harrykica84]

well what is a fgood sheet metal company?

[MORNE MEYER]

Hi, I have been working on chillers and dx units since 1997, and looking at the problem I would chemically clean the tube in tube heat exchanger. Disconect the water in and out pipes and using counter flow push chemicals through.
That should work.

[desA]

Agreed. Some manufacturers suggest installing CIP connections & valves, to allow chemical cleaning & reverse flushing.