After displaying the competitiveness of heat pumps in both the ecological analysis as in the economic analysis heating systems, even being really pessimistic about the average yield and the distribution schedule consumption for time discrimination rate, I will spend the next posts to deny or update old perceptions incorrect or outdated for heat pumps. Specifically I will focus more on the defense of the air / air (heat sink or heat source external air / heat source or destination of heat the air inside the house), either version split (split system: outdoor unit -more-compressor unit, usually within the typical console-) or multisplit (ditto with several interior consoles), either version falsotecho indoor unit (usually) with subsequent heat distribution ducts. The main advantage of the first is the reduced work to be placed, while the latter makes a better distribution of heat that a split simple for less money than a multisplit , but usually with a lower efficiency (less heat exchange surface interior and greater fan power requirement of having to push the air ducts) possible loss of heat in the pipes (not should be more than 15% as much). By far the duct system is the most popular in the U.S. in houses, for example.
should be noted that the technology in other heating systems and achieved only marginal efficiency improvements. In heat pumps, especially in the home, has not yet come to approach the maximum theoretical limit operation of a machine based on Carnot cycle. Really experimental machines could be built to much closer than at present, although that, today, the use of gas would be unsafe and therefore undesirable. Well, just improved compressor designs and improvements in performance and control, such as DC Inverter systems, has achieved almost double the efficiencies of these machines in the last 30 years.
Efficiency and defrost
Certainly, the efficiency of heat pumps with the outside temperature drops, or, seen upside down, the efficiency is the greater the less the difference between internal and external temperature (temperature difference).
Certainly, too, in this curve does not take into account the need for defrosting cycle heat pump, and the comment repeated over and over again says that in the defrost cycle loses much efficiency heat pump. Yes in the heat exchanger of the outdoor unit can start to form ice when we go down to 5 ° C, and yes that old pump defrost cycles performed (switch to air conditioning mode, though usually by stopping the fan units internal to melt the ice) newspapers below a certain temperature, and yes this was a considerably higher power consumption. However, this increased consumption, in studies of the 80 , trace it, at most, 20% (the average of the studies was 8%). This means that the number of kWh of heat inflated divided by the number of kWh of electricity consumed, it passes decremented by 1-1 / (1 +20%) = 17%, ie, if for example the COP-1 C 2.5 would be without defrosting, now would be (I stress, 20% are pessimistic) 2.5 x (1-17%) = 2'08 having to defrost periodically. However, modern heat pumps do not defrost newspapers, but the control unit detects the presence of ice and only then start a defrost cycle. Fall
performance with temperature
On the other hand, and although modern heat pumps can meet minimum operating temperature of -5 ° C to -20 ° C, there is the belief that subzero temperatures and performance is very low. Well, actually COP corresponding to -7 ° C is actually more like 2 / 3 of that for +7 ° C, ie if we have a heat pump with COP at nominal conditions (7 ° C ) of 4, the COP to -7 ° C will be closer to 4 x 2 / 3 = 2'66, or if we consider a pessimistic 20% increase in defrost, of 2'66 / 1'2 = 2'22. That is, even under these conditions the heat pump would be providing at least 2'22 kWh of heat per kWh electricity consumed. If we further assume that the temperature of -7 ° C or lower will take place at night, we take advantage of the TDH to compensate for the lower efficiency at the lowest cost per kWh.
Even in the possible situation where the heat comes not provided by the heat pump (have undersized, with few units or the same low power), we will support those nights in simple (and cheap) electric heaters (oil well , or halogen, or fan heaters) to which we can add in your plug one also inexpensive thermostat if it were built. Assuming that the heat was keeping x , then the overall efficiency would be along the lines of (2'22 + (x '22 -2)) / (1 + (x -2 '22) ), that x = 4 (to put something, if we are right sized for the nominal conditions of 7 ° C) would give us even a 1'44 kWh-calor/kWh-eléctrico efficiency, not bad value if you also Valley are paying the price.
Power output and efficiency
The POPs listed in the specifications of heat pumps is measured in nominal conditions of temperature and external humidity and temperature, is measured for a working power close to the maximum, ie close to be delivering all the heat as possible inside the house. Well, normal for a DC inverter heat pump is to be working at a point close to equilibrium, ie, delivering almost exactly the heat you're losing the house or room and therefore must be replenished, otherwise we undersized the heat pump, then it will be working to lower the nominal power, and therefore, at least one of the commercial models (have to see the specs sheet for each one in particular, to see if the ranges specified of power delivered and consumed, with which you can do calculation), this implies a greater efficiency at nominal COP. This stems directly from the reduced need to use fans in the indoor and outdoor units to exchange less heat.
For example, my heat pump split dual- , 4'35 have a COP of delivering rated power, but greater efficiency to 5 to deliver the minimum power. Conclusion
Even with moderately severe weather, while it does not involve freezing temperatures far beyond the nights (14 hour rate valley), using heat pump Hourly Rate Discrimination, supplemented by any radiators Electric, is a highly competitive both economically and ecologically.
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