efficient heat pump research
Proposals for more efficient heat pumps system
Introduction
FOREWORD
As an inventor, I look for more efficient solutions for thermotechnical systems such as heat pumps, heat exchangers, solar thermal panels and shallow geothermal systems, which today have too low efficiencies to really convince all people to buy them in the absence of a legislative obligation. Efficiency is considered as the ratio between the amount of thermal energy that the machine makes available and the energy it uses to operate (usually electrical energy). To understand, an electric stove that just transforms each unit of electrical energy into a unit of thermal energy, has an efficiency ratio of one. In the case of heat pumps, the efficiency ratio is called Coefficient Of Performance, COP. The Carnot cycle tells us that, for this type of machines, the theoretical maximum value of efficiency would have a COP value = 15 which means that, theoretically, these machines could capture an amount of thermal energy equal to 15 times the electrical energy they absorb to operate. This is possible because heat pumps do not transform electrical energy into thermal energy as an electric heater does, but use the energy given to them to capture and transfer heat from one environment to another. Although this theoretical maximum value is actually unattainable, the comparison with the current average COP efficiency values of heat pump appliances and systems for air conditioning, they show that, although they are more efficient in heating than boilers, they are still little efficient compared to what they could potentially yield. Let's take some examples.
- For very cheap air conditioning appliances consisting of two units, one external and one internal (split), for thermal powers of 8,000 - 12,000 btu with an average cost of 350 to 600 euros/dollars, the average efficiency value is COP = 3.
-For higher-end air conditioning appliances, consisting of two units, for heat outputs of 8,000 - 12,000 btu, the average efficiency value is COP = 4.
-For air-to-air or air-to-water heat pumps with a low condensing temperature of about 55- 65°C, with a sufficient thermal power for medium-sized homes, with an average cost of 6,000 euros/dollars, the average heating efficiency value is COP = 5.
- Monobloc air conditioners (with a single unit and therefore without an outdoor unit) with a thermal power of 12,000 btu, with an average purchase price of 600 to 1,400 euros/dollars have an average heating efficiency value of COP = 3.7 .
-For air-to-water hydronic heat pumps with high condensing temperature to power radiator or fan coil systems, the average heating efficiency value is just COP = 1.7. This low efficiency value is due to the fact that inducing a higher condensing temperature than the usual 55-65°C, in a heat pump system, for the operating needs of radiators, inevitably causes the system to lose efficiency.
- An absorption heat pump system with an aqueous solution of ammonia has an average efficiency ratio, and therefore a COP = 1.4 but in this case, it must be taken into account that a large part of the operating energy is not electrical but thermal and is therefore an efficiency value of about 47% higher than that of a simple condensing boiler that can recover 95% of the superior heat power of the fuel.
It is therefore clear that the efficiency of today's heat pumps can still be greatly improved. In the prior study of pre-existing patents, I have seen proposals for different refrigerant circuits, some with two compressors, with two or more expansion valves, or with an open circuit superimposed on the closed refrigerant circuit, but all for a modest gain in efficiency. The best solution I have seen among the existing patents, inserts a puffer with two heat exchangers, one that connects the condenser to the expansion valve and the other that connects the evaporator to the compressor suction thus increasing the temperature of the refrigerant liquid to be evaporated before it enters the evaporator and cooling the refrigerant vapor to be condensed before it enters the condenser, but even this solution only slightly increases efficiency. It is therefore perhaps better, to intervene on the four phases of a traditional loop circuit, improving a) the condensation process, b) the pressure reduction of the liquid refrigerant to be evaporated, which today is usually performed with an expansion valve, c) the evaporation process and d) the compression of the refrigerant and beyond this, e) heat exchangers can be created with a lower intrinsic internal thermal resistance. The development of each of these points can increase the efficiency of the system.
In the first series of patent applications filed on December 19, 2023, I increased the efficiency in points (a) and (e) by designing a more efficient condensation process for compression heat pumps and a condensation and absorption system for absorption heat pumps and a series of more efficient heat exchangers especially dedicated to heat exchange with air. I have precise ideas on how to intervene on the other points (b), (c) and (d) as well because I have spent 16 years developing solutions to all these points but they are topics that could not be covered in this first series of patents.
ADVANTAGES BROUGHT BY THE FILED PATENTS
With regard to point (a), the new condensation process, under the same physical conditions of temperature and pressure, speeds up the condensation of the refrigerant vapor by increasing the thermal power or, increasing the efficiency of the system because, if the same thermal power is maintained by condensing the same amount of vapor, through the reduction of the condensation pressure, the pressure difference between the evaporator and condenser will be decreased, reducing the work of the compressor and therefore increasing the efficiency of the system. Point (e) refers in particular to heat exchangers in which a fluid, such as refrigerant or water, exchanges heat with air . Today, in almost all cases, finned pack heat exchangers, microchannel heat exchangers or finned tube heat exchangers are used for heat exchange with air. In this type of heat exchanger, most of the heat exchange surface is made up of heat diffusion fins. This, for heat exchange, requires not only a temperature difference between the internal and external fluid, but also an additional temperature difference to induce a flow of heat to run through each fin. A cooler evaporator or a warmer condenser means a greater temperature difference between condenser and evaporator and since this leads to a greater internal pressure difference between evaporator and condenser, the efficiency of a heat pump system is always decreased. For this reason, under the same conditions and extension of the heat exchange surface, for the heat exchange between two fluids, it is advisable to use heat exchangers in which the separation surface between the two fluids coincides with the heat exchange surface, i.e. that there is no use of diffusion fins and this is just the opposite of what happens today in heat exchange with air. However, given the practicality and compactness of these heat exchangers, I later added to my patent application on the new condensing process, the figure described above, which shows how to use the new process also with the usual finned pack heat exchangers so loved by designers today.
REGARDING PATENT APPLICATIONS FILED ON DECEMBER 19, 2023
Initially, four patent applications were filed, the first for a new process of condensation and absorption of refrigerant vapor in heat pump systems, the second for a heat exchanger in the shape of a helix/cylindrical spiral which, in the case of heat exchange between air and refrigerant fluid or water, consists of three concentric tubes of large diameter to allow the passage of intense air flows, while, in the heat exchange between refrigerant fluid and water, it is externally the same as the previous one but has, in the central tube, a filling shape or a fourth concentric tube that serve to bring the flow of water closer to the surface of the tube. This allows for the continued use of large diameters useful for sustaining heat exchanges with low temperature differences, necessary to achieve high efficiency in heat pump systems. The third patent application concerns a heat exchanger that also has the function of a centrifugal fan and is used to cool or heat the air intended for a ventilation system. The fourth patent application joins the cylindrical helix heat exchanger with the new condensing process, also describing how the type of refrigerant circuitry suitable for this process, can be made and showing both appliances with two units and monobloc appliances. There have been complaints from the European Patent Office asking to respond to cases of prior art with pre-existing patents but I have been able to argue that the patents submitted are different thing. They also requested that the patent concerning the condensation/absorption process be split into two divisional applications and so it was done, specifying that, divisional patent applications diverge only in claims but an application was added that contained the technical drawing shown below. Having therefore satisfied the requests, it is very likely that the requested patents will be granted.
All patent applications referenced on this site are for invention patents and not for utility patents.
1Condensation process and absorption process of refrigerant vapour and related compression and absorption heat pump systems.
Original title in italian:
Processo di condensazione e processo di assorbimento di vapore frigorigeno e relativi sistemi a pompa di calore a compressione e ad assorbimento.
Originally filled on 19 Decenber 2023 in Italy and Switzerland with the codes: UIBM 102023000027114, and CH 001418/2023 .
After the request of the European Patent Office to split this patent application, on 11 October 2024 the UIBM 102024000022671 and the UIBM 10202400002692 were re-submitted, only for Italy, which differ from the original filed on 19 December 2023 only for claims and a third application was also re-filed, the UIBM 102024000022638 which, compared to the original, has the additional description of the application of the condensation process in the tank with cooling by means of common finned pack heat exchangers. These three patents will take the place of the original UIBM 102023000027114 approximately starting from September 19, 2025.
2Heat exchange systems using a helical heat exchanger.
Original title in italian:
Sistemi di scambio termico che utilizzano uno scambiatore di calore ad elica cilindrica.
Italian patent application no. 102023000027138 and Swiss Patent Application No. CH001419/2023 both filed on 19/12/2023 and remained unchanged.
3Heat exchanger with centrifugal fan function
Original title in italian:
Scambiatore di calore con funzione di ventilatore centrifugo.
Italian patent application no. 102023000027129 and Swiss Patent Application No. CH001420/2023 both filed on 19/12/2023 and remained unchanged.
4"SOFIA" system for compression or absorption heat pump.
Original title in italian:
Sistema a pompa di calore a compressione o ad assorbimento.
Italian patent application no. 102023000027162 and Swiss Patent Application No. CH001421/2023 both filed on 19/12/2023 and remained unchanged.
HOW THE DIAGRAM WORKS
Since the world of heat pump design refuses to abandon traditional heat exchangers with finned heat exchange surfaces like finned pack heat exchangers, microchannel heat exchangers or finned tube heat exchangers, I thought about this integration to my patent applications to allow the use of the new condensation process also with the use of these old types of heat exchangers. The figure illustrates how the condensation of the refrigerant vapour takes place in a tank, while one or more heat exchangers simply cool the internal liquid mass heated by the condensation of the vapour. The new heat exchangers described in the patents filed, to use this new condensation process, do not need this tank, and the condensation takes place inside the exchanger used as a condenser. So, let's explain how it works. In the current condensation process, the environment in which condensation takes place, is the internal environment of the heat exchanger, which is mainly occupied by the refrigerant vapour to be condensed, which condenses on the colder internal surfaces of the heat exchanger by pouring downwards from where, liquid comes out of the exchanger through the duct which, after the expansion valve, carries it to the evaporator. In the new condensation process, on the other hand, the internal volume of the condensing room is full, not with steam but with liquid refrigerant, in a similar way to how it is already in the evaporator. As already mentioned, only with regard to the specific case illustrated, the condensing environment is not that of a heat exchanger but that of a tank, because this allows the new condensation process to be applied with the use of conventional heat exchangers, while with the use of the heat exchangers described in the patent applications, the condensation of the refrigerant vapor takes place inside the heat exchanger. The inlet and outlet points of the refrigerant on the tank are connected by a short recirculation duct equipped with a small circulation pump. There may be a liquid-steam separator at the outlet of the tank because, if a higher heat power is required from the appliance or system, a greater quantity of steam can be pushed into the condensing tank and part of this steam may not be able to condense and in order not to accumulate, it will be necessary to remove it, connecting it to the compressor intake by means of a duct
equipped with a shut-off valve and a reduction device so that this way is only open when needed and does not cause too much pressure to be lost in the condenser. The condensation of the steam in the tank releases heat into the liquid mass which, in the case of heat exchange with air, can also be removed by conventional finned pack heat exchangers, as shown in the figure, or in the case of heat exchange with water, can be removed by plate heat exchangers and the extracted heat can, for example, heat hydronic systems with radiant surfaces. Let's examine the reasons for the increased efficiency of this condensing system. First of all, it allows a better penetration of heat through the heat exchange surfaces because the traditional system provides that the condensing environment is full of steam and a gas or steam that is immobile or moving very slowly in the heat exchanger, is a very poor conductor of heat while, in the new system, on the other hand, the condensation environment, It is filled with fast-flowing liquid due to the recirculation circuit. In the traditional system, the steam can only condense close to the surfaces of the exchanger. In the new system, on the other hand, the continuous recirculation of the liquid through the condensation environment, causes the liquid to cool and the vapor to be condensed coming from the evaporator, is blown and dispersed in a myriad of small bubbles in this cool liquid mass recirculating stream that enters the condensation environment and the vapor bubbles implode, condensing at every point of the internal volume of the condensation environment, which, let's remember, in this case is a tank. Since, in this case, condensation takes place in the tank, the heat exchangers connected to the tank only serve to cool the internal liquid mass and for this reason they can be common finned pack exchangers, or plate exchangers, if the cooling takes place with water instead of air. The figures, including those at the bottom of the drawing, illustrate how to prevent cooling vapour bubbles from entering the heat exchangers, or show how to effectively disperse the vapour into the liquid mass of the tank. Since the new process can condense steam faster, it can do what would happen with the traditional process if the heat exchanger had a higher overall thermal conductivity. Therefore, if the new condensation process involves a virtual decrease in the thermal resistance of the exchanger, or a virtual increase in its general thermal conductivity, then, if the system is not required to have more thermal power, it can afford to lower the condensing pressure, which will decrease the pressure difference between evaporator and condenser and the less effort required from the compressor will increase the efficiency of the system. In the event that the appliance or system includes the reversal of the functions from winter heating to summer cooling and vice versa, with an exchange of evaporator and condenser functions between the heat exchangers of the system, the system scheme must become symmetrical and the presence of a recirculation circuit makes the scheme a little different from the simple loop scheme (ring circuit consisting of the succession of condenser > compressor > expansion valve > evaporator > ) of current appliances and systems. It is all explained in the technical reports which I already sent by post to most of you perhaps three or four months ago. For a matter of symmetry, it is possible to repeat the same tank-heat exchanger scheme also at the evaporation side of the system and in that case, it will be sufficient to turn off the pump of the recirculation circuit and evaporation will take place both in the heat exchangers and in the tank. It is possible to make the evaporation take place exclusively in the tank if a lamination valve or in any case pressure reduction valve is placed, before the refrigerant exing from the exchangers, enters the tank because the fluid will thus be slightly overpressured in the exchangers due to the pressure of the circulation pump and the action of the aforementioned valve. With the same intent, the refrigerant could also be diluted with a different, heavier liquid, not intended for evaporation, which at the bottom of the tank would pass through the heat exchangers absorbing heat and then, falling like rain inside the tank, could pass this heat to the refrigerant which, heating up, would evaporate. The use of a dilution liquid allows the use of larger heat exchangers with a larger heat exchange surface. However, a real advantage caused by these choices, must be verified experimentally. To the scheme described here, however, I prefer the application of the new condensing process to the cylindrical helix heat exchangers described in my patent application that I will send you this time to an e-mail if you want to indicate me a contact address, preferably from one of your heat pump expert engineers who can evaluate it for you.