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The development of a high power density RAPID response on demand water HEATing technology

Final Report Summary - RAPIDHEAT (The development of a high power density RAPID response on demand water HEATing technology)

Executive Summary:
The aim of the RapidHeat project has been to create a high-power on-demand electric water heater.

On-demand water heaters are more energy-efficient than stored water heaters, particularly for applications where the hot water requirement is intermittent. Gas heaters for this purpose are widely available, but electrical on-demand heaters are not. A principal reason for this is that traditional electrical heating elements do not have the necessary speed of response.

The RapidHeat project planned to overcome this limitation by adapting a high power (25kW) electrical heater, developed and patented by Cressall for dynamic braking, which has a very fast (< 1 second) response thanks to its use of state-of-the-art ceramics and heat transfer methods. Taking Cressall’s patents as its starting point, the RapidHeat project would create a high power (75kW+) water heater, for use where gas is unavailable and there is a need for an intermittent hot water supply.

Water heaters that can produce large volumes of ‘instant’ hot water are particularly advantageous in commercial, industrial and public buildings. In such buildings peak demand for hot water can be many times the average and the cost of heat losses from the hot water stored to meet that demand is significant.

The aim of the project was to optimise the heating and control technologies for a 75kW RapidHeater, to manufacture prototypes for testing in ‘real world’ applications and finally to create a commercial product that the consortium partners could exploit to their individual commercial advantage.

During P1 we confirmed the choice of materials and construction for a 75kW RapidHeater, as demonstrated in Deliverables D2.1 D2.2 D2.3 D3.1 D3.2 and D3.3. We also established that the costs of uprating the electrical power supply to use such a RapidHeater would render it uneconomic in many of the applications that were originally conceived for it.

Therefore, the direction of the project changed in P2 towards the creation and testing of a smaller (3-10kW) RapidHeater, suitable for showers and vending machines. Because no on-site trials were now possible, the project Demonstration activities (Task 5 of the DoW) were adapted to reflect this and included testing work carried out by ISRI rather than the partners originally planned (TTMDI, Moragar and ADI).

We have created web site content, literature and press releases to explain the concepts and post-project activity will focus on finding industrial partners interested in partnering with members of the consortium to commercialise the RapidHeat technology.

Project Context and Objectives:
In the first nine months of the project we confirmed the choice of materials for a RapidHeater element (D3.1) and produced results that refine and validate the existing mechanical design (D3.2) in particular:

Encapsulation: Tecnalia’s work resulted in a suitable assembly and baking process for the element assembly that ensures that there are no inclusions in the Ceramic/Composite ‘sandwich’ after it has been fired to solidify the silicon carbide. (D2.2 D2.3)

Manufacturing of the Element:
There are two possible manufacturing processes for the ceramic element and the project established by testing that a properly encapsulated element made by the lower-cost ‘tape’ method (which has a 1.2-1.5mm maximum thickness) could be suitable (D2.1).

Leakage prevention
We have experienced pinhole leaks in the Chinese-made dough-moulded bodies for the EV2. The moulds belong to Cressall. In P2 this was investigated by ISRI and suggestions were made as to how to prevent this.

Life Testing
ISRI carried out accelerated life-cycle testing to establish the derating and MTTF for the EV2 when used with appropriate water/glycol concentrations in the ambient temperature range of -40°C to +45°C. (D5.1)

Cost Reduction
As a direct result of the work carried out during the project it will be possible to reduce the size, grade and thickness of the ceramic used, and also to reduce the number of springs needed, in a production RapidHeater.

Project Results:
The results from the project have confirmed the choice of materials and the mechanical design for a RapidHeater but have also clarified aspects of the market for these products that were not appreciated at the outset. The project could meet all but one of the target features of the proposed design: a RapidHeater is faster responding, smaller, lighter and has lower thermal losses than any existing designs, but not at lower cost. Having said that, cost improvements make the device more competitive than previously envisaged. The market for heaters of this type, which are sold mainly through specifiers (architects, consulting engineers, etc.) and building contractors, will not accept higher-performance higher-cost products without a very clear justification. We have not put our finger on a plausible justification, and furthermore there are clear technical and commercial reasons to think that we will not find one.

Our investigations of potential applications for the RapidHeater have come up against 5 serious issues:

Material cost
The use of high-cost materials, specifically aluminium nitride as the insulating medium and graphite for the heating element, will make the heater more expensive than equivalent sheathed element designs of the same nominal rating. AlN is two orders of magnitude more expensive by weight than the stainless steel used in sheathed elements, typically €8,000/kg versus €5-€15/kg for stainless steel; the slightly lower mass needed will in no way offset the higher costs of using this material. In the case of Cressall’s EV2 product, the light weight and low volume are the key benefits and so justify the use of the high cost materials against lower-cost sheathed element designs.

Operating voltage
Another attribute of AlN, its very high insulation resistance (>20kV/mm power frequency withstand), enables Cressall to produce brake resistors suitable for operation at medium voltages (3.3kV+) where sheathed elements cannot be used. For the RapidHeater, which will operate at mains voltages of 400-500V, this is not an advantage, so the expensive insulating material initially verified in RP1 may yet be substituted by lower cost alternatives that can still operate at 500V.

Infrastructure Costs
A RapidHeater would use a standard 400V three-phase supply. Simple physics dictates that this means it will need an input power of 75-85kW and a power supply rated at 125A continuous. A RapidHeater will almost invariably require cables and switchgear of a much higher rating than needed for the remainder of the installation. This problem was cited as a serious issue by several of the potential clients who we contacted, even after they had expressed initial enthusiasm for the concept.

Peak Demand costs
For an industrial or commercial business the use of instantaneous hot water heaters will raise their peak power demand; this number is key for the fixed elements of most business electricity tariffs. The main reason that stored water heaters are favoured over instant heaters is that the power demand is so high for instant heaters if they are to produce useful volumes of hot water. For example: a typical domestic heating installation will have either a 3kW electric immersion heater with a storage tank or a 30kW instantaneous heater and no tank. The tenfold increase in electrical power demand renders the instantaneous solution uneconomic.

Operating Costs
Electricity costs per kWh are typically three times as much as oil or natural gas, so electric heating of water is economic only if oil or gas are not available – and even where oil or gas cannot be used or are not available, stored water heating is still a less costly solution than point-of-use tankless.

For these reasons the focus in P2 has been the creation and testing of a prototype low-power RapidHeater suitable for shower and vending machine applications.

Potential Impact:
Many people rely on vending machines for tea and coffee and know the difference between coffee that has been made with freshly boiled water and one that contains pre-heated water. Existing vending machines require an accumulator filled with pre-heated water to overcome the delay between switch-on and the availability of water at the correct temperature; a RapidHeater would eliminate that need and provide freshly heated water at the appropriate temperature.

In addition to vending machine suppliers, white goods manufacturers and hot water tap providers also stand to benefit from the innovation. An instant hot water solution installed in the home offers customers a water and energy saving solution: the average UK household wastes 24 litres of water a day waiting for the shower to become hot enough.

The high power density of RAPIDHEAT also means the heater is smaller and lighter than other technologies on the market, which makes it useful for applications where space is limited, such as in the home.

TTMDI provided a high level of exposure within Turkey participating in many conferences and exhibitions.

Cressall, supported by ISRI, focussed its dissemination and exploitation efforts on engaging interested 3rd parties particularly within the electric shower sector. A number of opportunities have been identified which shall be prioritised during post-project commercial discussions.

Another advantage is that by removing the need for hot water reservoirs – the heater does not use a supply of preheated water – the heater cannot run out. Water heaters capable of producing large volumes of ‘instant’ hot water are needed in many commercial, industrial and public buildings and also in process and manufacturing industries that have intermittent demands for large volumes of hot water. These are cases where peak demand for hot water is many times the average, and the cost of heat losses from the hot water stored to meet that demand can be significant.

List of Websites:
Details of the project, the participants and the final press releases and leaflets are available at