We analyze the VRV System inverter heat pump

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Characteristics and functionalities of the inverter heat pump. VRV system.

Based on the study of energy certification, we provide this post with information related to the inverter heat pump before the facilities to better understand its operation and characteristics. Emphasizing the well-known COP and EER that characterize the inverter heat pumps.

There are different alternatives for air conditioning buildings. One of them is the heat pump, capable of providing cold air or hot air. In this post, I will try to explain what a system of air-to-air heat pump, and later the inverter and vrv system.

Also important is to understand what is the COP and the EER, to interpret which is the most efficient equipment, from the point of view of energy saving.

What is refrigerant

These systems are based on the operation of a traditional air conditioning unit. Surely you have heard the word refrigerant, and you have related it to the air conditioning of a car, a refrigerator, etc. But you will ask yourself, how can cold be produced with a refrigerant?

So that you understand, refrigerant is a fluid that has the facility to absorb heat at a low pressure and temperature, and yield it under high pressure and high temperature. To do this, we need that fluid to have special characteristics.

One of the main characteristics (among many others) is that it has a very low boiling temperature (change from liquid to gas). Next, and to give you an idea, I indicate different boiling temperatures (at atmospheric pressure):

  • Water… 99.98ºC
  • Ethanol … 78.37ºC
  • Ammonia…. -33.34ºC
  • R410A refrigerant… -51.58ºC

Imagine that we "enclose" this fluid in a pipe circuit (copper) and put it in contact with the environment that we want to cool; The refrigerant will absorb the heat and evaporate easily (remember the low boiling temperatures), which means that whatever is in contact with that part of the circuit will be cold. Therefore, the refrigerant is absorbing heat at low temperature and low pressure, changing state from liquid to gas. This part of the circuit is called the EVAPORATOR.

It is necessary to give up the heat absorbed by the refrigerant. To do this, the low pressure gas comes out of the evaporator. It is necessary that the pressure and temperature of the gas are high for the change of state to liquid, using the COMPRESSOR.

Once the pressure and temperature are raised, the refrigerant must transform into a liquid, that is, condense. This change of state is carried out in the CONDENSER, transferring the absorbed heat to the environment. In order to restart the cycle, it is necessary for the high pressure liquid refrigerant to lower it. To do this, prior to the EVAPORATOR, an EXPANSION VALVE is inserted.

To facilitate the evaporation and condensation process, air currents are used through fans, which are the ones that really accelerate evaporation by providing the necessary air flow. Similarly, a fan is included in the condenser to release the heat.

As a summary,stay with the idea that through the pipes in a closed circuit, a REFRIGERANT runs that absorbs heat in the EVAPORATOR (cold zone), and transfers heat in the CONDENSER (hot zone)

If you want to go deeper and understand more visually, I leave you some very interesting videos, where all these concepts are clearly explained.

What are heat pump systems

As seen above, we can provide cold air to a building unit, where the evaporator unit is located.

The heat pump, it can reverse the refrigerant cycle, thereby providing heat in winter (the interior equipment would act as a condensing unit and the exterior as an evaporating unit) and in summer it would provide cold (the interior equipment would act as an evaporating unit and the exterior as a condensing unit) . The outdoor unit / s incorporate the compressor.

Therefore, "playing" with the concept of evaporator and condenser unit, different heat pump systems can be configured:

  • Compact equipment: the old models that were installed in the windows
  • Split equipment: one outdoor unit and one indoor unit.
  • Multisplit equipment: one or more outdoor units and several indoor units

I would like to point out that all these systems are commonly referred to in Energy Certification software, as unizone or multizone DIRECT EXPANSION SYSTEMS.

There are many models of indoor and outdoor units, for domestic systems, residential, or tertiary buildings, we can see it in this article on types of air conditioning.

Have you ever seen cassette type units, duct units, decorative units, etc; therefore, there is a great variety of products, to be able to air-condition from a home, to a hospital. I recommend that you visit the manufacturers' websites, and take a look at the catalogs; in them you will discover a multitude of technical characteristics and uses of the equipment.

What is an inverter system

As we have seen, to increase the temperature and pressure of the refrigerant gas, it is necessary to existence of a compressor.This important element is the main consumer of electrical energy in an air-to-air heat pump system.. And what did the manufacturers think to reduce the energy consumption of this equipment? Well act on the operation of the compressor.

In the air conditioning systems Conventional room temperature control is carried out with a thermostat that acts by stopping and starting the equipment, and consequently the compressor, with which the electricity consumption peaks are very high. It is called all-nothing systems.

The inverter system or as many call it, the inverter equipment, acts on the compressor by varying its speed, adapting to the thermal needs demanded, for which, by means of a frequency variator, we avoid continuous starts and stops. They are called proportional systems.

The two main advantages of an inverter system are:

1. - Comfort.

- The setpoint temperature is reached much faster than in a conventional system
- Maintains the desired temperature with less expense and minimal excesses of cold or heat
- Lower noise levels

You can see in this graph, the large temperature fluctuations in a conventional system (fixed speed), while in inverter systems they are very small (+ 1 / -1ºC approximately)

2. - Energy Savings

- We avoid constant compressor starts and optimize energy production
- Less maintenance due to the reduction of mechanical wear of the compressor.

What is a VRV system

The initials of theVRV system mean "Variable Refrigerant Volume", although the precise term for the VRV operation would "Variable refrigerant flow".

Unlike the conventional heat pump, this system has the ability to vary the flow of refrigerant supplied to the evaporation-condensation batteries, thus more effectively controlling the temperature conditions of the premises to be air-conditioned. This sounds like us, doesn't it?

Clear. All the systems called INVERTER are VRV systems, although in advertising, the first term is used for the domestic and residential market.

Therefore, when we talk about a VRV system, we will think of a tertiary building with numerous outdoor and indoor units. Each indoor unit will work independently of the others, requesting the amount of refrigerant it needs. An electronic expansion valve will allow the necessary amount of refrigerant fluid to pass through.

A certain number of indoor units will "hang" from each outdoor unit, taking into account the manufacturer's limitations in terms of thermal powers and pipe distances, among other variables.

What is a VRV system with heat recovery

As we have seen previously, the evaporation of the refrigerant fluid to cool a room implies its condensation and the transfer of heat to the outside environment. This heat of condensation is usually wasted towards the outside in air-to-air systems. Systems withheat recovery They allow you to take advantage of that heat to another place where heating is required.

Let's imagine a building with a glass facade facing south and another facing north. Let us suppose a day in which the outside temperature is low, but that from noon on the south façade the sun shines directly. Perhaps, the rooms on the north façade demand heat, and the rooms on the south façade (due to the indices of the sun and high occupancy) demand cold. Until a few years ago, with a conventional VRV system, we would only have the possibility of providing heat or cold.

The VRV systems With heat recovery, they allow us to provide heat and cold simultaneously, "transporting" the refrigerant in the gaseous state from the evaporating units to the heating units, producing gas condensation there. Then the condensed liquid will return to the evaporating units.

This intelligent distribution of the refrigerant fluid is carried out through a sophisticated electronic control system.

Therefore, a VRV system with heat recovery has the advantages of a VRV system with the addition that heat can be transported from room to room without wasting it.

What is the COP in the EER

The COP and the EER of a heat pump, we they will indicate the efficiencies of the equipment working in heat or cold respectively.

The energies involved are the electrical power consumed by the compressor (W), the calorific power supplied by the condenser (Qc) and the calorific power absorbed by the evaporator (Qf). The principle of conservation of energy requires that:

If we consider that the objective is to provide heat, the useful energy of the heat pump is Qc. The energy that we will use to produce Qc is W. Thus the heat efficiency of this machine would be:

We observe that we have called COP to the efficiency of the heat pump. The initials COP, are the initials in English "Coefficient of Performance", which can be translated by coefficient of performance.

Let's imagine that the COP of a heat pump is 3.5. This means that each electrical kWh is transformed into 3.5 kWh of heat. An electric stove, for example, transforms 1 kWh of electricity into 1 kWh of heat. Look, therefore, at the efficiency of heat pumps.

Similarly,if we consider that the objective is to provide cold, the useful effect is the heat extracted from the cold bulb.

Although in the expression, it appears as COP, it is actually calledEER (Energy Efficiency Ratio), and it is always lower than the COP in heat.

Therefore, with these two values, we will get an idea of the efficiency of the heat pump that we are studying. Next, I show you some graphics of the labeling of air conditioning equipment according to the COP and EER.

What would be the conclusion

Currently, as we have seen, there are some Inverter and VRV air conditioning systems, very advanced, in which electronics have made these equipment very efficient systems with enormous advantages, even with the possibility of heat recovery, which makes them very competitive from the point of view of energy saving. Therefore, they are systems to take into account when air conditioning any type of building.

Article prepared by Paulino Rivas García (Industrial Technical Engineer - Installations / Energy Efficiency Engineer) Owner of http://www.instalacionesyeficienciaenergetica.com/ in collaboration with OVACEN.

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