Cooling with Hydronics

By Roy Collver

As the world gets warmer due to climate change, air conditioning has become a necessity in areas it used to be considered a luxury. After experiencing the so-called “heat dome” early last summer, HVAC contractors even here on the west coast have been swamped with calls to add cooling to existing buildings, many of them currently heated by hydronic systems. People still want hydronic radiant floor systems and other specialties in new-build homes, but now have air conditioning on their list of must haves. How can the hydronics industry rise to the challenge?

This article will cover the options currently available, touching on some potentially new ideas, and developments in the residential and light commercial sectors. Energy of all types are going to continue to increase in cost, putting operating efficiency neck-and-neck with greenhouse gas (GHG) emission reduction requirements.

Choosing the right method may be quite obvious in many cases, but there will often be nuances in building design and occupant usage that will rule out cookie cutter solutions. Restrictions presented by structural details, building code requirements, aesthetic demands and of course, client budget will all impact decisions. Ducted forced-air systems for instance may be far too intrusive physically, leaving hydronics to provide some satisfying solutions.

Limited options
In retrofit situations where the current structure is primarily heated by hydronics, options may be limited. New structures have the benefit of cooling and ventilation integration during the design phase, allowing much more flexibility. Basic cooling approaches are spot cooling of zoned occupied areas with individual cooling devices, distributed cooling via refrigerant, chilled water or air from a central cooling device, and multi-pronged approach using a variety of cooling methods and energy efficient building design.

By far the most popular method used today for mechanical cooling, electricity is used to operate chillers, heat pumps and air conditioners. In retrofit systems, the install cost goes from the simple and economical installation of window shakers to spot cooling with mini split air conditioners all the way through to full blown hydronic chilled water distribution systems. Look closely at SEER ratings and provide the most efficient equipment the client can afford.

Although window shakers and through the wall air conditioners may be the affordable options for those who are on a tight budget and are willing to put up with noise and uneven cooling, upgrading to a professionally installed mini-split or multi-split system is deal. Some very good portable/seasonal DIY mini splits are available, but they have limited capacity, and need to be installed, uninstalled, and stored seasonally. The small portable DIY units that supply and vent air outdoors have lousy efficiency and are not recommended.

Hydronic central cooling systems that use air handlers and/or fan coils can usually be upgraded with either DX coils or chilled water coils for whole building coverage. Ground source, air source and water source heat pumps are making significant inroads into the hydronics industry as we decarbonize. By adding a chilled water buffer tank from a reversible heat pump to supply a hydronic system, a huge opportunity for technicians to get into the cooling business has opened up. Central chilled water hydronic distribution through small diameter piping can be very easy to conceal, even with four-pipe heating/cooling systems.

Caution
Before venturing into chilled water hydronics, designers and installers need to be fully educated in the design details. Any component that might drop in temperature below the dewpoint must be insulated, and those components that intentionally create condensate must be designed to drain it away. These are the details most beginners get wrong.

I have lately seen the re-introduction of absorption chillers and heat pumps using ammonia as a refrigerant and a gas flame as a way to evaporate the ammonia. Unfortunately, they just don’t make much sense when we are trying to decarbonize our built environment, but there may be some applications where insufficient electrical supply for compressive devices could favour their use.

Water is used to chill air as it evaporates and can be used to directly cool indoor air in the right environment, but there are few places in humid Canada where they are a good idea. In dry air places where they do work, potable water is often in short supply — a situation that is not improving.

Geothermal solution
Pumping cold deep lake water up from 30 feet deep or more directly into heat exchangers is being done commercially here and there. Toronto uses lake water for cooling downtown buildings, but the process for gaining approvals is long and complicated. Residential applications are rare but can be an option with the right combination of building location and lake access. Also, using drilled-well ground water in some areas may be allowed, but geo-exchange using heat pumps and heat exchangers is much more common where people have sufficient real estate to be able to dump heat into the ground or water.

New ideals
All of the technologies discussed above use significant energy for cooling, but there are some new and old ideas that can help cut deeply into the utility bill. The conservation route is always preferred to reduce cooling load and make it easier to cool with less intrusive equipment while reducing energy use. Many new ideas are coming at us from the commercial world, where every watt of energy used is scrutinized, but some ancient ideas are getting a close look as well. A building is a complete system. And looking only at the HVAC equipment is bound to result in sub-optimal energy reduction results.

Often overlooked as a cooling option, natural and mechanical ventilation when outdoor air temperatures drop, or indoor air temperatures rise can significantly reduce the need for mechanical cooling. Look at the details of some older buildings (cupolas, transoms, openable windows) to get ideas. Ventilation devices are easily automated with modern controls. Simple and effective, shading to reduce solar gain will also cut back the need for energy intensive cooling and can also be easily automated.

Radiant cooling might sound like science fiction, but it is a real thing. New developments in coatings have been found to promote radiation of heat from a building roof to outer space, stay tuned on this one.

Decoupling humidity control is not the current practice of latent heat removal being used in dedicated outdoor air systems such as chilled beam cooling. Another “stay-tuned” idea — scientists are working with substances and techniques to dry out air prior to sensible cooling, thus avoiding the energy cost of latent heat removal. Experiments with liquid and other desiccant materials are looking promising.

There is much to talk about in these times where cooling is becoming an urgent need for many. Developments are coming at us very quickly and it is going to take some effort to keep up with them. Who knows what is going on in secret labs all over the world? If you stay on top of the research and development being done today and learn as much as you can about hydronic cooling, it is clear to me you will be able to leap-frog over your competitors as the phones keep ringing. :