Buzz Words Explained

What is a Heat Pump? || Are Heat Pumps Loud? || What is COP? || What does my unit need to defrost?
How do I size a Heat Pump? || Do I choose Ground Source or Air Source? || Low or High Temperature?
What is the Boiler Backup? || Inverter? || What is Weather Compensation?

What is a Heat Pump?

A heat pump is, in essence, a fridge! 
We are all accustomed to refrigeration as part of our everyday lives. Each day we put our dairy, vegetable and meat products into the fridge to keep them cold. Similarly in the Air Conditioning process we cool the air in a room in order to make conditions more comfortable for us; this heat is then rejected outside as a waste product. 

Now consider this process in reverse; instead of us regarding the heat that is rejected as a waste product imagine that it is useful. We remove “heat” measured in Kilowatts (kW) from either the ground or the air and put it into water, this water is circulated around the house for home heating; this the essence of a Heat Pump.

Are Heat Pumps Loud?

A Nexa heat pump will make less noise than a standard fridge! Our 11 kW unit has a sound pressure measurement of 39 db(A) which would make it inaudible outside a closed bedroom window.

What is COP?

This stands for Co-efficient of Performance and is an indication of the energy efficiency of a refrigeration unit. It is the ratio of energy in to energy out. For instance our 11 kW heat pump has a COP of 4.17. This means that under a set of internationally agreed conditions 1 kW of electricity in will result in 4.17 kW of heat output. This makes heat pumps one of the most efficient ways of heating you home, cheaper in fact than Oil, Gas or Wood Pellets.  COP is a very useful way of comparing one Heat Pump product with another but be aware, it is only half the story. Without effective heating controls a low COP is meaningless.

What does my unit need to defrost?

Under certain conditions you get a build up of ice on the outside of an Air Source heat pump. As heat is removed from the air, moisture will condense on the cooling surface of the outdoor unit. As the air temperature drops below 0oC  a layer of frost can build up on the heat transfer surface which, if left unchecked, will  insulate the heat collection surface and dramatically reduce the unit’s performance. As you would expect from a world leader in heat pumps technology, Carrier have taken this into account when they designed their range of units.

Firstly, Carrier heat pumps are designed to be tall and thin with low cross sectional areas through the heat collection coils. This characteristic “Tombstone” style design means that we are only taking 3oC from the outside air as it passes through. This characteristic allows us to run at a much lower temperatures than units from other manufacturers without the unit starting to ice up.
Secondly, when frosting does start to occur, Carrier uses a system of smart controls to removes the ice before it ever becomes a problem. Sensors located inside the Heat Pump are continually measuring refrigerant pressures and air temperatures in much the same way as a modern car will continually monitor engine performance and will make adjustments as necessary. Eventually when the performance has deteriorated sufficiently and ice has started to build up, the heating process will be stopped and the unit will run for a couple of minutes in reverse or until all the ice has been melted and the coil is dried off.

Both the 30RHX range of Air Source Heat Pumps and the XP Energy Inverter ranges are designed to operate in our climate and all performance figures quoted reflect this reality.

How do I size a Heat Pump?

We would always recommend that you get a properly qualified Engineer to carry out a load survey on your building. Rule of thumb is not good enough when sizing heat pumps and adding 10% here and 20% there to cover all eventualities may result in comfortable conditions for you and a sense comfort for the installer but could prove costly. An initial investment measured in the hundreds of Euro could save you thousands of Euro in the long run.

When sizing a Heat Pump the following aspects must be taken into consideration:

Is it necessary to cover 100% of cooling needs in summer time?
If “Yes” then the heat pump will be sized for its cooling capacity.

Is there any existing boiler, or is a boiler used for the heating of hot domestic water and can this boiler be used as back up for the coldest days?
This would allow the downsizing of the heat pump and thereby provide a more competitive option.

One of the most common mistakes made in choosing a heat pump is to select a unit which is capable of dealing with the total heating load, including over-sizing, at the minimum local temperature.

If you then take into account the local climate profile you will find that the number of days requiring full capacity are very few indeed (Weather Data recorded by Met Éireann over the last 10 years has shown that Ireland has had fewer than 10 days per annum below 0°C and very rarely does the temperature drop below -3°C). The result of sizing for worst case / full load capacity is that other than on the coldest day of the year you will have a massively oversized system with a large Heat Pump, a high volume buffer tank in the Hydronics Module and electrical supplies that are way over sized.

Do I choose Ground Source or Air Source?

The local climate, total investment costs and energy savings when compared with others energy sources are the main determining factors in choosing the most suitable heat pump type for your installation. Using Carrier’s selection software we can calculate all of the above but as a rule of thumb carrier recommend that  ground source heat pumps are appropriate for use in homes where the outside air temperatures goes  under -10°C for a minimum time of 10 days. As Carrier offer both Air Source and Ground Source units and are experts in refrigeration we are confident in offering this advice.

Low or High Temperature?

As each type of heat emitter will have it’s own operating range the selection of system will be dependent on your system as a whole. Under floor heating typically is designed to operates at a maximum of 35oC at minimum outside temperature whereas radiators will require a higher temperature (65°C) under the same conditions. It is therefore apparent that the choice of heat pump technology will depend on the choice of terminal units. It should be noted however that the lower the operating temperature of the heat pump the lower the running cost, regardless of which  ever technology you choose.

What is the Boiler Backup?

With an existing system it is possible to retain an existing boiler. If the boiler is in good condition it can be used as a back up to a medium-temperature heat pump providing domestic hot water and taking over from the heat pump for the coldest days of the year. It is a simply a question of economics. And for the future? Our range of  hydronic modules include units that come complete with electrical back up heaters;  if the  boiler should eventually fail of the cost of oil / gas becomes prohibitively high your system will continue to work without any additional investment.

Inverter?

An inverter is a device which makes it possible to change the running speed of a motor. When applied to a refrigeration compressor it provides the potential for substantial energy savings by matching the output from a heat pump to the heat demand in a house. They are ideally suited to systems using under floor heating. Carrier DX units are all fitted with inverter controls as standard.

What is Weather Compensation?

Whatever the heat pump technology, the lower the leaving water temperature, the higher is the energy efficiency achieved. By matching the temperature leaving the heat pump to minimum water temperature required to heat the building (Weather compensation) heat pumps achieve remarkable energy efficiencies. Nexa have refined this further however. Unlike most manufactures Nexa are pioneers in the area of heating controls and have developed a system that not only adjusts  the water temperature in accordance to outside conditions we also adjust for inside conditions. This means that we get better efficiencies out our systems than our competition can get from theirs. All this at a reasonable cost to the end user too.