It is not surprising the bad reputation of heat pumps when working in heating mode. In this type of systems of ac heat mode, there are a couple of concepts that should be taken into account at the time of installation if we do not want to have problems when winter comes. One of these terms causes a sensation of low comfort and discomfort.
AC heat mode
With the systems of heating by air is very common that, in cold days, the mass of warmer air stays in the superior part of the premises and the cold one in the inferior part, giving rise to a quite unpleasant sensation of “cold feet”. It happens because the hot air has a lower weight than the cold air. Therefore, if nothing prevents it, it will be placed on our head, in the highest part of the room.
In heating, the indoor units of this type of systems operate by taking ambient air, heating it, and then driving it to the premises again. The problem comes when the team takes air from the top of the room and pushes it back to the top, this creates a mass of hot air in the upper part of the room that could only benefit us if we were the spiderman himself.
What is the solution?
The equipment type mural (or wall) is the most economist, but they are also one of the main causes of this effect, since its small dimensions make the intake and drive of air are close together, in addition to the scope of the “air jet” “It’s not usually enough to cover the whole place.
A possible solution would be to install an interior equipment type floor, which would take air from the lowest part of the room, forcing down to the mass of hot air that is above. So, it would create a flow of air from top to bottom that it would benefit us when it comes to combating stratification.
Also, there would be other possibilities, such as installing an air distribution system through ducts and grilles, placing the air intake grille in the lower part of the room.
Lack of power at low outside temperatures
Another reason why these types of equipment tend to be “thrown away” is the low performance they offer with outside temperatures below 5ºC. If the person who installs the equipment calculates thermal loads “at eye level”, it is possible to install a device whose nominal power is adjusted to the demand of the room, but do not take into account that the power offered by the equipment with external temperatures losses may be less than the nominal value indicated by the manufacturer.
They could sell us a heat pump with nominal power 19.8kW thinking that it is enough for our room but, as you can see in the underlined part in yellow, the day that the outside temperature is 0ºC the equipment could only offer 14.3kW. If it has not been taken into account, it could “leave us lying” just when it is most needed (colder days).
The heating heat pump can be a very efficient and comfortable system, but two basic concepts must be taken into account for heat mode in ac solutions: stratification of hot air and performance at low outdoor temperatures. If these two things are overlooked, it is possible that we will not have problems in the milder days (more than 5ºC outside), but almost certainly, it will not work correctly in the coldest days.