Hydronic and steam systems

Hydronic heating systems are systems that circulate a medium for heating. Hydronic radiant floor heating systems use a boiler or district heating to heat water and a pump to circulate the hot water in plastic pipes installed in a concrete slab. The pipes, embedded in the floor, carry heated water that conducts warmth to the surface of the floor, where it broadcasts heat energy to the room above.

Hydronic systems circulate hot water for heating. Steam heating systems are similar to heating water systems, except that steam is used as the heating medium instead of water.

Hydronic heating systems generally consist of a boiler or district heating heat exchanger, hot water circulating pumps, distribution piping, and a fan coil unit or a radiator located in the room or space. Steam heating systems are similar, except that no circulating pumps are required.Hydronic systems are closed loop: the same fluid is heated and then reheated. Hydronic heating systems are also used with antifreeze solutions in ice and snow melt systems for walkways, parking lots and streets. They are more commonly used in commercial and whole house radiant floor heat projects, whereas electric radiant heat systems are more commonly used in smaller "spot warming" applications.

Heat pumps

In mild climates a heat pump can be used to air condition the building during hot weather, and to warm the building using heat extracted from outdoor air in cold weather. Air-source heat pumps are generally uneconomic for outdoor temperatures much below freezing. In colder climates, geothermal heat pumps can be used to extract heat from the ground. For economy, these systems are designed for average low winter temperatures and use supplemental heating for extreme low temperature conditions. The advantage of the heat pump is that it reduces the purchased energy required for building heating; often geothermal source systems also supply domestic hot water. Even in places where fossil fuels provide most electricity, a geothermal system may offset greenhouse gas production since most of the energy furnished for heating is supplied from the environment, with only 15–30% purchased.

Environmental aspects

From an energy-efficiency standpoint considerable heat gets lost or goes to waste if only a single room needs heating, since central heating has distribution losses and (in the case of forced-air systems particularly) may heat some unoccupied rooms without need. In such buildings which require isolated heating, one may wish to consider non-central systems such as individual room heaters, fireplaces or other devices. Alternatively, architects can design new buildings which can virtually eliminate the need for heating, such as those built to the Passive House standard.

However, if a building does need full heating, combustion central heating offers a more environmentally friendly solution than electric-air central heating or than other direct electric heating devices. This stems from the fact that most electricity originates remotely using fossil fuels, with up to two-thirds of the energy in the fuel lost (unless utilized for district heating) at the power station and in transmission losses. In Sweden proposals exist to phase out direct electric heating for this reason (see oil phase-out in Sweden). Nuclear and hydroelectric sources reduce this factor.

In contrast, hot-water central heating systems can use water heated in or close to the building using high-efficiency condensing boilers, biofuels, or district heating. Wet underfloor heating has proven ideal. This offers the option of relatively easy conversion in the future to use developing technologies such as heat pumps and solar combisystems, thereby also providing future-proofing.Typical efficiencies for central heating are: 85-97% for gas fired heating; 80-89% for oil-fired, and 45-60% for coal-fired heating.^[8]

Body heat

About 250,000 people pass through Stockholm's Central Station each day

Body heat is not an energy source that normally springs to mind when companies want to keep down soaring energy costs.

But it did spring to the mind of one Swedish company, which decided the warmth that everybody generates naturally was in fact a resource that was going to waste.

Jernhusen, a real estate company in Stockholm, has found a way to channel the body heat from the hordes of commuters passing through Stockholm's Central Station to warm another building that is just across the road. "This is old technology being used in a new way. The only difference here is that we've shifted energy between two different buildings," says Klas Johnasson, who is one of the creators of the system and head of Jernhusen's environmental division.

"There are about 250,000 people a day who pass through Stockholm Central Station. They in themselves generate a bit of heat. But they also do a lot of activities. They buy food, they buy drinks, they buy newspapers and they buy books.

Excess body heat

All this energy generates an enormous amount of heat. So why shouldn't we use this heat. It's there. If we don't use it then it will just be ventilated away to no avail."So how does the system work in practice?

Heat exchangers in the Central Station's ventilation system convert the excess body heat into hot water. That is then pumped to the heating system in the nearby building to keep it warm. Not only is the system environmentally friendly but it also lowers the energy costs of the office block by as much as 25%.

"This is generally good business," says Mr Johansson. "We save money in energy costs and so the building becomes worth more.

"We are quite surprised that people haven't done this before. For a large scale project like Kungbrohuset (the office block) this means a lot of money."

Over the next 40 years, most experts agree that the supply of oil and gas will become less abundant.

There will be strong competition and higher prices for the resources that remain. Given the abundance of human body heat worldwide and the growing need for renewable energy to replace costly fossil fuels - is this Swedish idea going to catch on?

Costs and benefits

Stockholm's Central Station is one building reusing heat from passengers passing through.

"People are now starting to think about urban heat distribution networks everywhere," says Doug King, a consultant specialising in design innovation and sustainable development in construction.

"But the financial costs and the benefits will depend very much on the climate and the pricing of energy in a particular country."

He explains that harnessing body heat works particularly well in Sweden because of their low winter temperatures and high gas prices.

Spin offs

"It means a low-grade waste heat source, like body heat, can be used advantageously. It's worth them spending a little bit of money on electricity to move heat from building to building, rather than spending a lot on heating with gas."Mr Johansson is hoping there will be a lot of spin offs from their idea at Stockholm Central Station: "To get energy usage down in buildings what we need to do is use the energy that is being produced all around us.

"We own both Central Station and Kungbrohuset along with the land in between. So we are in charge of all of it and that has made it easier for us. But this doesn't mean that it cannot be done otherwise. It just means that real estate owners have to collaborate with each other."

He also advocates sustainability. "It's important in Sweden. But it should be important everywhere. Sustainability is the key ingredient to the future of mankind. We need to get sustainable with energy if we are supposed to live on this planet for a long time to come."

But what about the Swedish commuters in the station - will they be the ones left out in the cold?

"The commuters won't get chilly because we don't steal energy from Central Station we use excess heat that was already there before," says Mr Johansson.

So, with its freezing winters, green credentials and high energy costs, Sweden takes a creative approach to heating.

To stay warm all they need to do is keep the heat on. And, if Stockholm's Central Station stays busy then for one building at least it is well on the road to a low carbon and energy secure future.

The need for modern mechanical systems is one of the most common reasons to undertake work on historic buildings. Such work includes upgrading older mechanical systems, improving the energy efficiency of existing buildings, installing new heating, ventilation or air conditioning (HVAC) systems, or--particularly for museums--installing a climate control system with humidification and dehumidification capabilities. Decisions to install new HVAC or climate control systems often result from concern for occupant health and comfort, the desire to make older buildings marketable, or the need to provide specialized environments for operating computers, storing artifacts, or displaying museum collections. Unfortunately, occupant comfort and concerns for the objects within the building are sometimes given greater consideration than the building itself. In too many cases, applying modern standards of interior climate comfort to historic buildings has proven detrimental to historic materials and decorative finishes.

This Preservation Brief underscores the importance of careful planning in order to balance the preservation objectives with interior climate needs of the building. It is not intended as a technical guide to calculate tonnage or to size piping or ductwork. Rather, this Brief identifies some of the problems associated with installing mechanical systems in historic buildings and recommends approaches to minimizing the physical and visual damage associated with installing and maintaining these new or upgraded systems.

Historic buildings are not easily adapted to house modern precision mechanical systems. Careful planning must be provided early on to ensure that decisions made during the design and installation phases of a new system are appropriate. Since new mechanical and other related systems, such as electrical and fire suppression, can use up to 10% of a building's square footage and 30%-40% of an overall rehabilitation budget, decisions must be made in a systematic and coordinated manner. The installation of inappropriate mechanical systems may result in any or all of the following:

• large sections of historic materials are removed to install or house new systems.
• historic structural systems are weakened by carrying the weight of, and sustaining vibrations from, large equipment.
• moisture introduced into the building as part of a new system migrates into historic materials and causes damage, including biodegradation, freeze/thaw action, and surface staining.
• exterior cladding or interior finishes are stripped to install new vapor barriers and insulation.
• historic finishes, features, and spaces are altered by dropped ceilings and boxed chases or by poorly located grilles, registers, and equipment.
• systems that are too large or too small are installed before there is a clearly planned use or a new tenant.

For historic properties it is critical to understand what spaces, features, and finishes are historic in the building, what should be retained, and what the realistic heating, ventilating, and cooling needs are for the building, its occupants, and its contents. A systematic approach, involving preservation planning, preservation design, and a follow-up program of monitoring and maintenance, can ensure that new systems are successfully added--or existing systems are suitably upgraded--while preserving the historic integrity of the building.

No set formula exists for determining what type of mechanical system is best for a specific building. Each building and its needs must be evaluated separately. Some buildings will be so significant that every effort must be made to protect the historic materials and systems in place with minimal intrusion from new systems. Some buildings will have museum collections that need special climate control. In such cases, curatorial needs must be considered--but not to the ultimate detriment of the historic building resource. Other buildings will be rehabilitated for commercial use. For them, a variety of systems might be acceptable, as long as significant spaces, features, and finishes are retained.

Most mechanical systems require upgrading or replacement within 15-30 years due to wear and tear or the availability of improved technology. Therefore, historic buildings should not be greatly altered or otherwise sacrificed in an effort to meet short-term systems objectives.

Date: 2014-12-22; view: 1217