Domestic Hot Water: An Overview

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Domestic hot water heating is the heating of water for personal use. It can eat up quite a lot of energy.

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In many homes across the globe, water heating can consume about 10-30% of all the energy being used in the home. Although this will often depend on the number of inhabitants, the lifestyle these inhabitants lead, and the house type.

It’s a good idea to keep in mind that heating your water will often consume a large portion of the household’s energy. For instance, people in Canada use around 75-liters of hot water every day to clean themselves, wash their clothes, wash their dirty dishes, and general cleaning

That is a lot of water and heating, leading to high electrical bills. You can repurpose, recycle or replace old water heaters.

The energy sources used in most water heaters are usually the same as what you’ll find in most space heaters, though this isn’t always true.

The most common energy sources include oil, propane, natural gas, and, of course, electricity. Each of the sources mentioned has its unique drawbacks and benefits. For example, most electric heaters need no ventilation. However, they can’t work when there’s no power.

Furthermore, they use way more primary energy compared to natural gas. Heaters fueled by natural gas need adequate ventilation and airflow, but they use way less energy and heat up much faster.

Propane has the same advantages natural gas has; however, this type of fuel needs scheduled delivery and is a lot pricier.

You can reduce your total costs by selecting water heaters that are more energy efficient. You can also keep costs low by reducing the heating load via drain-water heat recovery devices or use less hot water.

When choosing a water heater, you must think about how much money it’ll cost you to operate the product or the “second price tag.”

Sometimes it’s way more cost-effective to buy a more energy-efficient, pricier model because it’ll end up saving you a lot more money in the long-term.

Water Heating Methods

Water Heating Methods

All water heaters generally use some fuel as a power source. This power is then used to help turn cold water into hot water.

There are many different types of water heaters out there, and we’re going to look at some of the most common ones below. You can use these independently. However, sometimes they can be combined into other existing systems.

Storage Tank Water Heaters

Storage water tank heaters are the water heaters you’ll find in most homes. Water is heated in these water heating units and then stored in a tank readily available whenever anyone wants to use it. When you open a hot water tap in the home, the hot water from the storage tank is what’s made available to you.

The used water is then replaced by cold water that flows into the storage tank. Water temperature is maintained by the thermostats that are on the burners. The water heater units are equipped with both a pressure and a temperature relief valve to ensure they’re safe.

These water heating units can be inefficient sometimes; however, their energy efficiency can be increased if you minimize standby losses or reduce the amount of combustion heat needed to heat the water, which you can do by reducing the heat losses from the heater’s chimneys or vents.

Tankless Water Heaters

As its name suggests, a tankless water heater is a water heater that heats flowing cold water hence doesn’t need a storage tank. It only heats water when needed. It helps increase efficiency by getting rid of standby losses.

Most on-demand electric water heating units can’t supply all the hot water needed by the entire household, making them not ideal for that kind of application. But, many other gas-fired tankless water heater units can provide enough water for the whole house at any time.

Gas-fired models are often mounted on a wall outside the house, making it easier for them to vent out the fuel gases.

Heat Pump Water Heaters

A heat pump water heater uses electricity to capture the heat in the air and then uses that to heat the water. These heaters don’t directly convert electricity to heat water. The air in the room where the water heater has been placed is used as a heating source by the device.

One major issue these heaters have is in addition to using the heat that’s in the air around them. They also tend to suck up humidity, which can sometimes become uncomfortable. However, during the summer period, heat removal can prove beneficial.

However, you might want to consider switching to a space heater in the winter instead of this.

Solar Water Heaters

Water heaters can also use energy from the sun to heat water. Heaters that can do this are known as solar domestic water heaters. Okay, these are generally not used exclusively by themselves and instead are used to provide around 65% of the home’s hot water needs.

These water heating units have storage tanks, solar collectors, and a circulating pump. Normally, most people use them to preheat water and then use a conventional heater afterward.

Domestic Hot Water Systems

In simple domestic hot water systems, as the water stored in the collector gets hot, it becomes lighter, expands, and moves upward to the top of the storage tank.

It then draws in heavier, cooler water from the bottom. It results in a natural thermosiphon circulation. This development gradually heats all the water in the tank.

This circulation has been known to exhibit self-regulating tendencies. This simply means that they’ll adjust in flow rate so that the temp increments from inlet to outlet stay at approximately 10K.

This heating system needs the storage tank to be slightly higher than the collector. In most cases, especially if it’s been exposed to outdoor weather conditions, you’ll need to ensure the tank has been well insulated so that you can avoid undue tank heat losses.

If the storage tank can’t be placed in an elevated position for one reason or the other, you’ll need to introduce a small pump to drive fluid circulation. You must then control the pump, for instance, by using a differential thermostat.

It then becomes a forced circulation system, which is classified as active. On the other hand, the thermosiphon system is well-known and accepted by most as a passive system.

You can get cold water directly from the mains, although in this case, all the components involved need to have the ability to withstand the pressure that comes from the mains. You can also get water from a feeder or storage tank, which should preferably be in an elevated position, and use a float valve to get water from the mains.

When it comes to the pressure from the mains, most water supply or utilities, authorities need folks to install non-return valves.

Whereas low-pressure storage tank systems have a vent pipe that gives them access to the atmosphere, mains pressure systems need protection against overpressure via a pressure relief valve because of the water’s thermal expansion when being heated.

This relief valve will also protect the device from imploding/collapsing, usually caused by a vacuum formation.

In places prone to freezing, the system needs protection against frost damage. In mild winter weather conditions, where freezing rarely occurs, you can sacrifice a little heat by slow water circulation.

You can use drain-back systems in cold climates as well. These systems automatically drain the water in the collector when it gets to freezing temperature.

Alternatively, you can also use an indirect system to fill the primary circuit with an antifreeze solution, like propylene glycol or ethylene, or with non-aqueous liquids. In this closed circuit, a heat exchanger is water transmits the heat to the consumable water.

If you’re using a toxic anti-freeze agent, then you might need a double-walled heat exchanger to be safe. Such safety and control devices can complicate an otherwise simple, straightforward system.

How To Control Domestic Hot Water Systems

How To Control Domestic Hot Water Systems

Whether your boiler is staging or modulating, or it’s a complete standalone system, there are many sophisticated heat-timer controls out there that can help in energy management. You can even get heat timer controls that have an Electronic Tempering Valve. Different factors will determine what kind of control you’ll need.

Electronic Tempering Station

This control system uses a pre-plumbed solution by incorporating a motorized electronic tempering valve. This 3-way motorized mixing valve contains a control computer placed as far out as five-hundred feet from the valve.

Multi-MOD Controls

For domestic hot water units that need several boilers modulating stage controls, multi-MOD controls can help you set precise points while auto-rotating load balancing stages. These controls often contain comprehensive internet and mobile device remote management, wireless sensors, and outdoor reset capability.

HWRQ Controls

These controls can operate both multiple boiler stages and multiple boilers. They can be used as controls for DHW priority options or standalone DHW systems. When used to control heating, there’s outdoor reset capability for maximum thermal efficiency.

HWR Controls

These controls are for single hot water boiler applications used for domestic hot water heating and building heating. These controls can help you manage domestic hot water priority and help and provide you with maximum efficiency by giving you complete control over your domestic hot water pump.

Wrapping Up

Domestic hot water units have become very popular over the last few years. Countries like Israel and Japan have been using solar-based domestic hot water systems for quite some time now, and they have shown to be both reliable and practical.

For example, Japan currently has over 3 million domestic hot water systems.

However, the one major disadvantage of passive domestic water heaters is that the water in the tank or transfer heat fluid can freeze up during the winter seasons. With that said, it’s a problem that’s been solved in recent years, making it not so much of an issue.

All in all, this type of heating system has emerged as the top choice for most homeowners all across the globe. Yes, most of them use quite a lot of energy, but they’re all worth it. Hopefully, now you know all you need to know about domestic hot water systems.

References:

EnergyEducation.ca

ScienceDirect.com

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