This instructable documents a simple electrical circuit for saving energy by reducing the stand-by natural gas consumption of a combi boiler. A combi boiler is a device for the supply of residential spatial heating and domestic hot water demand. The main condition for successfully applying this instructable is that in the design of the combi boiler the use of an external switch has been foreseen. Both modern technology combi boilers and older installations might be prepared for it. This instructable proposes a wired solution, a low-tech design without wireless technology.

Financial payback times of half a year or less can be realized at low investment costs. One can expect to need a working time of two hours to two days to do the tests and to install the switches as described in this instructable.

Note that safety restrictions apply and that a few additional conditions must be met (see step 2 in this instructable).

After measuring your own combi boiler stand-by and cold start consumption, and comparing this with your average daily domestic hot water demand pattern, you’ll be able to calculate the benefits of applying the concept from this instructable to your combi boiler. Generally speaking, the smaller your house is, the larger the relative benefits will be. If you don’t use hot water a lot, benefits of omitting stand-by losses will be higher. The higher the natural gas prices you pay (including energy taxes), the more benefit you’ll experience from the energy savings. You may expect net annual savings of $ 7 to 24 per year in the United States, EUR 10 to 36 in the average European Union and EUR 12 to 43 in the Netherlands.

The concept of the circuit described here is made available through a Creative Commons Attribution license (CC BY); the innovative part of the design is explained in step 1 below. For commercial use some directions have been provided in the last section of this instructable (step 8).

Step 1: Introduction

A combi boiler (or combination boiler) is a device for the supply of residential spatial heating and domestic hot water demand, usually run on natural gas and designed for a single dwelling. The part of the system that prepares the domestic hot water can have considerable stand-by losses and consequently significant stand-by energy consumption. I have observed that when such a heating device is being installed in new houses, the manual control (if available) of the hot water preparation system often is not connected. This means that the hot water preparation system is always simply 'on', having hot water available instantly, which results in stand-by losses. Heat is leaking away from the hot water vessel continuously and natural gas is being used at intervals during the whole day, even when no hot water is being tapped. Modern technology combi boilers might be equipped with an 'automatic mode', which might be an energy-saving mode or a self-learning timer-mode. However, I think that more energy reduction is possible when the device is fully controlled manually (this depends on your typical daily use pattern though). Some combi-boilers are equipped with an instantaneous hot water supply system. These might have no stand-by losses, although I expect that some will also be kept at operational temperature, resulting in stand-by losses.

The concept described in this instructable is new and innovate because of three aspects:

1. Using a multiway switching layout allows controlling the combi boiler from two locations in a building, typically the kitchen and the bathroom/shower of a house, or from two different floors. The main advantage is that the combi boiler can be controlled independently from two different rooms, and that the LED provides feedback to the user on the status of the device;

2. The control switch and/or indicator LED is being placed directly at the hot water tap, which is where you need it. Standard installation (if in use at all) usually locates a single switch at the thermostat in the living room. The main advantage of the concept described here is that it is made easier for the user to switch off the hot water when it isn't needed anymore;

3. The complete installation can be performed with simple material like switches, cables and LEDs, available in local stores.

The aim of applying the concept in this instructable is to reduce internal heat losses in the combi boiler and thus to reduce stand-by natural gas consumption.

Combi boilers are very common in Europe. In a recent study by the Energy research Centre of the Netherlands (ECN) an analysis of energy-saving measures has been performed (http://www.ecn.nl/publications/ECN-E--12-013, May 2012, with a summary in English). From this study it can be observed that in the Netherlands the penetration of (condensing) combi boilers is 96% in single and multi-family houses (based on a population of 146 thousand dwellings). This high penetration may be typical for the Netherlands, but it is not for most other European countries. The report also documents the expected average efficiency of the domestic hot water production in a combi boiler, which may vary between 59% and 67,5% (the latter for a condensing type of system, both efficiencies based on the gross calorific value of natural gas). Reasons for these relatively low efficiencies are the stand-by losses and the pipe losses. The concept introduced in this instructable helps to reduce these losses and to increase the overall efficiency.

The realized energy savings will depend on the user demand, i.e. how often hot water is consumed during a typical day. In the next steps I show that significant annual savings per year can be expected if all conditions are met. It is important to measure some characteristics of your combi boiler to estimate the maximum realizable savings. See step 4.

This instructable works for a natural gas-fired condensing combi boiler that is prepared for manual control of the domestic hot water functionality. Apart from safety restrictions (see step 2) also technical conditions apply.  There are two main conditions: the combi boiler must be prepared for an external switch, and you'll need the installation manual of the boiler. The easiest situation is when domestic hot water demand only occurs at two locations in the house (or on two floors). This situation is described in this instructable, using two three-way switches. Installing more switches is possible as well, but this will require a special switch (a four-way or intermediate switch).

As there is quite some information to share, the listing of the required material comes in under step 6 only. In summary: you will need the combi boiler installation manual, two three-way switches, some meters of electrical cable (both with 2 and 3 wires) and two LEDs in the voltage level that you'll determine in step 5 of this instructable, and optionally a casing for integrating LEDs. In step 7 an alternative circuit layout with reduced functionality is introduced, which will be much quicker to install.
<p>This is cool! I'd love to see you submit this to our Nest challenge on good.is. You could win a Nest and save energy in your house even more! http://homeplanet.maker.good.is/. Let me know if you apply at community@goodinc.com. Thank you :)</p>

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