WO2025105968A1

WO2025105968A1 - Heating system for hot tub or pool

Info

Publication number: WO2025105968A1
Application number: PCT/NO2024/050249
Authority: WO
Inventors: Kenneth SLEIRE
Original assignee: Individual
Current assignee: Individual
Priority date: 2023-11-15
Filing date: 2024-11-14
Publication date: 2025-05-22
Anticipated expiration: 2026-05-15
Also published as: NO20241128A1

Abstract

A heating system for a hot tub or pool is described, wherein the heating system comprises: - a water inlet and a water outlet; - a circulation pump to circulate the water from the inlet to the outlet; - a combustion heater for heating the water between the inlet and the outlet; - a pipe to conduct exhaust gases away from the combustion heater; and - a control unit to control the heating and the water circulation. Also described is a hot tub or pool comprising such a heating system.

Description

HEATING SYSTEM FOR HOT TUB OR POOL

The present invention relates to a heating system for a hot tub or pool. The invention also relates to a hot tub or pool comprising such a heating system.

The hot tub and pool industry has seen steady growth over many years but the global increase in electricity prices, particularly during recent years, has created challenges for private and commercial users alike. The costs of heating large volumes of water have become a significant burden, which has led many people to cut back on the use of their hot tubs, or to take them out of service temporarily in order to avoid high costs. This is true especially of people who use their hot tubs more sporadically, for example at their cabin, where there is a need for rapid and efficient heating on arrival, but also for rental businesses, which often have to change the water between tenants and have limited time to ready the hot tub again. In addition to costs, the time required to heat the hot tub is a significant challenge, especially for rental businesses. For example, it takes 14 hours on average to heat up a 1200-litre hot tub from 8.5 degrees to 38 degrees using a standard 3 kW electric heating element.

The traditional technology used for heating hot tubs and pools is based on electric heating elements with a power output of around 3 kW (variants from 1.5 to 4 kW). These systems are well suited for smaller hot tubs but when tub size grows, it leads to a significant increase in heating times, which in turn leads to higher electricity bills and impaired user friendliness. Although upgrading with more heating elements is an option, it means significant additional costs, both in terms of purchase and installation.

Previous attempts to address these challenges have involved the use of external combustion heaters, such as diesel or gas heaters, central heating, or heat pumps. However, these solutions involve complex installations that many users are unwilling to accept. In addition, these systems have been prone to significant heating losses due to how the water is transported between the systems and hot tub, where it is conducted out of the hot tub to be heated before being returned. The object of this invention is to remedy or reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to the prior art.

This object is achieved through the features specified in the description below and in the claims that follow.

In a first aspect, the invention relates to a heating system for a hot tub or pool, wherein the heating system comprises:

- a water inlet and a water outlet;

- a circulation pump to circulate the water from the inlet to the outlet;

- a combustion heater for heating the water between the inlet and the outlet;

- a pipe to conduct exhaust gases away from the combustion heater; and

- a control unit to control the heating and the water circulation.

The combustion heater can typically have a power output of 2 kW or higher, depending on the size of the hot tub or pool. In some embodiments, the combustion heater may have a power output of 5 kW or higher. The combustion heater typically comprises an air inlet and a combustion chamber where fuel is burnt. The combustion chamber can profitably be designed for optimalisation of combustion efficiency and thermal density. Also the air inlet can profitably be integrated with the heating system and the hot tub or pool, allowing the air entering the combustion heater to be warmed up/preheated, which may contribute to higher efficiency and reduced heating time.

The combustion heater utilises an efficient air-to-water principle, where the energy from a fuel, for example biodiesel, is combusted and converted into heat that is transferred to the water. The supply of fuel initiates the process by transferring fuel from a fuel tank to the combustion chamber. The fuel tank, which can be either internal or external depending on the installation, stores the fuel and has a capacity that depends on the energy consumption of the system and the desired time of operation. In one embodiment, an electric fuel pump is used, ensuring even and precise supply of fuel to the combustion chamber, controlled through valves keeping the fuel pressure stable. Fuel is injected into a combustion chamber through an injector or nozzle, which atomises the fuel to ensure even and efficient combustion.

The combustion chamber protects the surrounding components from heat, while ensuring good energy conversion. To initiate the combustion, an electric ignition system may be used, which may comprise a glow plug or a glow element. This ignition system ignites the fuel on start-up, and after ignition the combustion is maintained through the continuous supply of both fuel and oxygen.

In one embodiment, the heating system may comprise an air supply system where a fan pulls air into the combustion chamber. This will increase the supply of oxygen to the combustion heater. The air may be preheated if taken from inside the hot tub, which will contribute to more efficient combustion.

The combustion heater comprises an internal heat exchanger as the central element to transfer heat from combustion to the water. Once the fuel is ignited in the combustion chamber and produces heat, the hot combustion gases are conducted into the internal heat exchanger. The water to be heated flows through the channels in the heat exchanger. When the combustion gases pass through these water channels, they emit heat to the water, and subsequently the gases are cooled down before being conducted out through the exhaust system.

In one embodiment, the control unit can control the combustion heater so that it always works at full power or is switched off, which may ensure rapid heating and make it easy for users to achieve the desired heating without the need for manual adjustment of the combustion process. The combustion heater can be driven by various sources of energy. In an advantageous embodiment, it can run on biodiesel as an environment-friendly option. Biodiesel is a renewable fuel with lower emissions than traditional diesel and contributes to reduced environmental impacts. One further advantage of biodiesel is that it is compatible with most combustion systems and can provide stable and reliable heat output. In alternative embodiments, diesel may be used, which is readily available and reliable, or propane or natural gas, which provide high heating efficiency and are cleaner relative to diesel.

The heating system can preferably be designed with flexibility in mind, so that the combustion heater can readily be adapted to various types of fuel. This enables the user to choose source of energy based on costs and availability, while retaining heating efficiency.

In one embodiment, the heating system can further comprise a heat exchanger, where the pipe to conduct exhaust gases away from the combustion heater is connected to the heat exchanger. In this way, hot exhaust gases/exhaust can be used to preheat the water before it is conducted into the combustion heater, thereby significantly increasing the efficiency of the heating system. This will reduce the energy consumption and/or heating time.

For example, the heat exchanger can be designed using a material that is corrosion resistant and resistant to chlorine and bromine, especially if used in a hot tub or pool exposed to such chemicals. In one embodiment, the heat exchanger can be made of stainless steel, for example SS316L. In addition to having high resistance to the above chemicals, SS316L has good thermal conductivity and thus ensures efficient transfer of energy from the hot exhaust gas to the water. SS316L is also less prone to carbon precipitation at high temperatures, which ensures the steel retains its structural integrity even during intense heating loads. This is especially important in heat exchangers exposed to high temperatures from the combustion heater. In an alternative embodiment, the heat exchanger can be made wholly or partly of titanium. This may, for example, be relevant if a combustion heater with very high output is going to be used, which may result in particularly heavy loads on the heat exchanger.

The pipe conducting exhaust gases from the combustion heater to the heat exchanger may preferably be insulated so as to prevent/mitigate heat loss. For example, the pipe can be a metal pipe, such as a steel pipe.

In one embodiment the heating system may further comprise an electric heating element. The heating element may be used to increase the heating capacity further by supplementing the combustion heater. When the hot tub has reached the desired temperature, the electric heating element can take over for the combustion heater. The same applies if there is a need for replacement or maintenance of the combustion heater, as discussed above. The hot tub may then be used temporarily with electric heating only.

In one embodiment, the electric heating element can be integrated with the control unit, so that they make up an electric heating module, which may be advantageous for optimal control of the electric heating element. The same control unit may then preferably be equipped with ports for control of the circulation pump and combustion heater. In a non- restrictive embodiment, the control module can be of a Gecko in.YE3 type with a 3-kW electric heating element. Similarly, the control system can then be of a Gecko in. grid type with user control via Geek in. touch or similar.

Gecko in. touch 2 is a wireless communication module which allows remote control of the entire system via a mobile app. Through the in. touch 2 app, the user can control all functions of the hot tub, including adjustment of heating mode, water treatment, temperature settings, and accessories.

In. touch 2 is especially useful in the heating system in order to offer the user the flexibility to remotely control the combustion heater, to activate it before arrival, or to monitor the temperature. The app may preferably support push notifications so that the user is alerted of any changes in hot tub status, which contributes to user friendliness and efficiency.

The heating system may comprise one or more sensors that communicate with the control unit. The sensor(s) can be of a temperature sensor, pressure sensor and/or flow sensor type. The control unit can be controlled via a panel that is integrated with the hot tub or pool and/or be remotely controlled via a computer or mobile application. In one embodiment, the control unit can be at least partially autonomous. For example, a user may set a desired temperature, while the control unit, based on feedback from a temperature sensor, may heat the water until the desired temperature has been reached and subsequently maintain the temperature at the desired level. The control unit may also regulate the output of the circulation pump if a deviation from a desired water flow is detected.

In one embodiment, the heating system may comprise one or more valves to regulate the volume of water circulating through the combustion heater between the inlet and outlet. One of these valves may be a main control valve controlling the primary flow of water in the system. This valve may be fine-tuned to control how much water flows into the combustion heater and any electric heating element, contributing to balanced heating. By placing the main control valve centrally in the system, for example downstream of the heat exchanger and the control module and upstream of the combustion heater, the heating system ensures stable operation, where the volume of water can be adjusted to the capacity of the combustion heater and the heating requirement of the hot tub.

In one embodiment, the heating system may further comprise one or more service valves enabling the entire water flow between the inlet and outlet to bypass the combustion heater. The service valve(s) may be positioned so as to enable maintenance without the need to completely empty the water from the hot tub. This is particularly useful if the combustion heater needs repair or replacement, as the water flow can be redirected without shutting down the entire system. By closing the service valves, the hot tub can still be used while performing maintenance on the combustion heater. This will reduce downtime and increase user friendliness by ensuring the hot tub is available even during repairs. At least one service valve can thus profitably be positioned in a branch point downstream of the control module and heat exchanger, allowing the water to circulate directly into the hot tub or pool and/or through the combustion heater.

In a second aspect, the invention relates to a hot tub or pool comprising a heating system according to the first aspect of the invention, wherein the heating system is integrated with the hot tub or pool. The hot tub could, for example, be a massage or bubble type spa, while the pool, for example, could be a counter-current type pool, though not restricted thereto.

In one embodiment, the hot tub or pool may have an inlet connected to the heating system outlet and an outlet connected to the heating system inlet. The water in the hot tub or pool will then be able to circulate via the heating system until it reaches the desired temperature.

The fuel tank may be integrated with, or be positioned outside, the hot tub or pool. In both cases it may be connected to the combustion heater by a fuel pipe/hose.

Described below are examples of preferred embodiments illustrated in the accompanying drawings, wherein:

Fig. 1 shows a schematic heating system and a hot tub according to the invention;

Fig. 2 shows a front view of an alternative embodiment of a heating system according to the invention; and

Fig. 3 shows a side view of the heating system in Figure 2.

In the following, reference number 1 will be used to denote a heating system according to the first aspect of the invention, while reference number 10 will denote a hot tub comprising such a heating system 1. In the figures, the same or corresponding elements are indicated by the same reference numbers. For the sake of clarity, some elements may in some of the figures be without reference numbers. The arrows show the direction of flow of water and exhaust gases.

Fig.1 shows entirely schematically a simple embodiment of a heating system 1 with a hot tub 10 in the background, for illustration purposes only. The heating system 1 may also be used with various types of hot tubs and pools, including counter-current pools, where active heating is utilised. The heating system 1 has an inlet 2 for water. Inlet 2 will typically be connected to a not shown outlet from the hot tub 10. Similarly, an outlet 4 from the heating system 1 is connected to a not shown inlet to the hot tub 10, so that the water in the hot tub circulates through and is heated by the heating system 1, which is integrated with the hot tub 10. Only if the hot tub is empty or the water is going to be fully or partly replaced, will there be a need to connect an external water supply and drains.

Water circulation between the inlet 2 and outlet 4 is driven by a circulation pump 6. The circulation pump 6 is integrated with the hot tub 10 and thus ensures an even flow of water and favourable heat transfer. From the inlet, the water flows through a heat exchanger 8, through a control system/unit 12 with an electric heating element 14 and further to a combustion heater 16. The control system 12 and the electric heating element 14 are integrated with a joint control module 15. The heating system 1 is connected to a not shown external electricity supply through a power cable 18. A not shown external control panel is further connected to the control system 12 with an electric heating element and the combustion heater via control cables 20. It should be understood that the control system and/or combustion heater may also be wireless. In the embodiment shown, the combustion heater 16 has an air inlet 22 integrated with the hot tub 10, while the combustion heater 16 is connected to an external fuel tank 24, preferably through a standardised quick-release coupling via a fuel pipe/hose 26. The supply of fuel to the combustion heater 16 is controlled by a fuel pump 28, which in the shown embodiment is integrated with the hot tub. From the combustion heater, a pipe 30 conducts exhaust gases away from the combustion process. The inlet 31 to the exhaust pipe 30 is connected to the combustion heater 16, while the outlet 32 is connected to the heat exchanger 8, allowing the heated exhaust gases to flow alongside and transfer heat into the water from the inlet 2. Cooled exhaust gases are then conducted away from the heat exchanger 8 by means of an external exhaust gas pipe 34 that extends from the hot tub 10 and preferably has an outlet at a distance and/or direction that ensures it will not cause any discomfort to a hot tub user. Hot water from the combustion heater 16 flows through a hot water pipe 17 and into the hot tub 10 via the outlet 4 to the heating system.

Fig. 2 shows, also entirely schematically, a second embodiment of a heating system 1 according to the invention. The heating system 1 according to Fig. 2 is provided with a main control valve 38, a first service valve 40 and a second service valve 42. In the shown embodiment, the first service valve 40 is positioned in a first pipe branch 44 directly downstream of the control module 15, while the second service valve 42 is positioned in a second pipe branch 46 downstream of the first pipe branch 44. The main control valve 38 is positioned between the two pipe branches 44, 46. Through operation of the control system 12, the various valves 38, 40, 42 will interact to regulate the water flow between the inlet 2 and the outlet 4. The first service valve 40 may be closed completely, allowing the entire water flow to bypass the combustion heater 16. This can be practical in a situation where the water in the hot tub 10 has already reached the desired temperature, or where the combustion heater 16 is about to be serviced. The hot tub 10 may then still be used with electric heating even if the combustion heater has been removed for repair. Similarly, the second service valve 42 may be closed, fully or partly, to regulate the volume of hot water flowing out of the combustion heater 16 to the outlet 4 of the heating system 1. In a situation where the first service valve 40 is fully closed, all the water from the control module 15 will flow directly to the outlet 4 into the hot tub, instead of flowing upwards in the first pipe branch 44 into the combustion heater 16. All valves may also be positioned in intermediate positions between open and closed for fine tuning of the water flow. In the shown embodiment, the hot water pipe 17 extends from the combustion heater to the second pipe branch 46 upstream of the outlet 4. During bypassing of the combustion heater 16, the second service valve 42 may also be closed.

Fig. 3 shows a side view of the heating system 1 from Fig. 2, focusing on the heat exchanger 8. Upstream of the heat exchanger 8 it is connected to the inlet 2 of the heating system 1 via the circulation pump 6. At the opposite end, the heat exchanger 8 has an inlet 50 connected to the outlet 32 of the exhaust gas pipe 30. The hot exhaust gas from the combustion heater 16 flows into the inlet 50 through the heat exchanger 8 parallel to, but in the opposite direction of and separated from, the water. The exhaust gas pipe 34 conducts the cooled exhaust gas away from the hot tub 10. Preheated water now flows out from an outlet 52 in the heat exchanger 8 and further into the control module 15, as shown in Fig. 2.

The applicant has tested the hot tub 10 shown in Figs. 2 and 3 holding 1200 litres of water. The time required to heat the water from 8.5°C to 38°C was approximately 5 hours, which is a reduction of 9 hours compared to a traditional hot tub with an integrated electric heating element.

A person skilled in the art will understand that the figures are principle sketches only. The relative proportions of individual elements may also be distorted.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference numbers placed between parentheses shall not be construed as limiting the claim.

Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be profitably used.

The control unit may be implemented by means of hardware comprising multiple distinct elements, and by means of a suitable computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware.

Claims

C l a i m s

1 . Heating system for a hot tub or pool, wherein the heating system comprises:

- a water inlet and a water outlet;

- a circulation pump to circulate the water from the inlet to the outlet;

- a combustion heater for heating the water between the inlet and the outlet;

- a pipe to conduct exhaust gases away from the combustion heater; and

- a control unit to control the heating and the water circulation.

2. A heating system according to claim 1 , wherein the heating system further comprises a heat exchanger, and where the pipe conducting exhaust gases away from the combustion heater is connected to the heat exchanger.

3. A heating system according to claims 1 or 2, wherein the heating system comprises one or more valves to regulate the volume of water circulating through the combustion heater between the inlet and the outlet.

4. A heating system according to claim 3, wherein at least one of the valves is a service valves allowing the entire water flow between the inlet and outlet to bypass the combustion heater.

5. A heating system according to any of the preceding claims, wherein the heating system further comprises an electric heating element.

6. A heating system according to claim 5, wherein the electric heating element is integrated with the control unit so that they make up a heating module.

7. A hot tub or pool comprising a heating system according to any of the preceding claims, wherein the heating system is integrated with the hot tub or pool.

8. A hot tub or pool according to claim 7, wherein the hot tub or pool has an inlet connected to the heating system outlet and an outlet connected to the heating system inlet.

9. A hot tub or pool according to claims 7 or 8 comprising an integrated fuel tank for the combustion heater.

10. A hot tub or pool according to any of the preceding claims 7-9, wherein the combustion heater is connectable to an external fuel tank.