Water under the bridge?
Is VRF just water under the bridge?
We have experienced over the last few years’ global electronics manufacturers taking over major European Chiller/HVAC manufacturers to gain access to the advanced water technologies now in development and in turn the future potential markets that will inevitably be available.
The objective of this article is to remind you that Hydronic water technology has been used for superlative heating and cooling in commercial buildings for decades. This historic, deep-rooted and highly lucrative approach is, in part, based on the thermal properties of water.
No other heat transfer material provides the flexibility, safety, reliability, energy efficiency or environmental compatibility of water!
What’s the big deal? After all we take the Hot and Chilled Water systems for granted, don’t we?
Over the last few decades, a new method for moving thermal energy through buildings appeared and become the main product of choice for both consulting engineers and contractors in the UK. This method uses refrigerant as the transport media throughout a building and is known as a Variable Refrigerant Flow system.
So what comes out on top? Are there advantages and disadvantages to both?
ASHRAE produced a document ‘Water beats VRF’and decided to showcase both systems in its Atlanta headquarters and meter their performance.
Their conclusion was: –
‘Four reasons to choose a Hydronic System over VRF’
- Easier to install and maintain
According to ASHRAE, VRF systems involve lots of refrigerant pipe and use oil for compressor lubrication. Control of oil return is critical. Special care in installation is necessary to ensure that contaminants don’t enter the system and damage the compressor. Then there’s all the copper piping, refrigerant tubing and fabrication of brazed joints required. Proprietary VRF systems therefore require specialized technicians, and building owners are dependent on the manufacturer for the life of the system.
Chilled water systems are easier to install and maintain. Their piping runs don’t require brazing or special soldering; plumbers and pipe installers can handle the job, and there’s no oil or refrigerant to deal with.
- Lower life cycle cost
According to ASHRAE, building owner can expect to get significantly lower life cycle cost out of a Hydronic system. A VRF system lives a much harder life and consumes more energy; especially in the winter. The compressor is installed in a complex field installed refrigerant system. Furthermore, it requires a very specialized mechanic. Compare this to a factory packaged heat pump or chiller in a Hydronic system. They are much simpler refrigerant systems and have a proven track record of longer life than a VRF system. Hydronic systems are more efficient, cost less to install and live a much longer life.
Lower first costs
According to ASHRAE, Hydronic chilled water systems have generally been regarded as costing more to install. But that’s no longer true. Today’s advanced Hydronic systems include application of technologies like integrated and single pipe systems that dramatically reduce piping, along with the use of variable speed pumps and fans. These help bring the first costs of a chilled water system in line with a VRF system.
- More Energy Efficient
According to ASHRAE, Energy efficiency claims by VRF manufacturers have been difficult to verify, and without actual test data in hand it’s been difficult to determine the actual facts. The ASHRAE building comparative energy usage study shows that a VRF system is not as efficient as a geothermal system. In all cases, new variable speed Hydronic chillers and heat pumps outperform variable speed VRF.
HVAC system designers, architects, and building owners have options when it comes to heating and cooling buildings. The choice of the system should have the following considerations such as up front costs, operating costs, long-term serviceability, expandability, reliability, safety, and environmental impact responsibility. Of course each project should be based on its merit. The simple fact is that both have their obvious merits but water is vastly under rated and specified in comparison.
After reading with interest ASHRAE’s findings we considered what additional benefits that modern Hydronic systems offer relative to VRF systems – just to put the cat amongst the pigeons of course you understand!
Hydronic systems can be used with many energy sources and the systems are simply adaptable to a wide variety. Such energy sources include Boilers powered by natural gas, propane, or fuel oil, Geothermal and Air-to-Water Heat Pumps, and Renewable Energy heat sources such as Solar Thermal collectors and Biomass boilers. Other potential heat sources include waste heat recovery, off-peak thermal storage systems and Combined Heat and Power (CHP) systems. In some cases two or more of these heat sources can be combined in the same system and share the load based on the most positive operating conditions for each.
VRF systems are generallyexclusivelyobtainedby electricity!
Hydronic systems allow for simpler future modifications. When aged commercial buildings are improved, the existing Hydronic distribution system (or parts of that system) may be reusable in combination with a new central plant for producing hot and cold water.
When VRF systems are used, the existing piping and terminals must either be decommissioned in place or removed from the building. All new copper piping and refrigerant-based terminal units must then be installed to each conditioned space. This can be highly disruptive to the normal use of the building and uneconomical.
ASHRAE covered the point of piping however Hydronic systems reduce risks associated with refrigerant leaks. It is possible for a leak to develop in either a Hydronic heating/cooling system, or a VRF system. A leak in a Hydronic system is generally easy to detect and the material leaking is just water or a mixture of water and glycol. Well-designed Hydronic systems provide numerous isolation valves that allow the portion of the system where the leak is to be isolated from the remaining parts of the system. Hydronic systems that distribute heating or cooling energy produced by a refrigerant-based source can be designed so that the refrigerant-containing devices are confined to a mechanical room, or located outside the building.
A leak in a VRF system is a serious and potentially dangerous. VRF systems contain much more refrigerant compared to Hydronic systems served by a typical heat pump or direct expansion chiller. Under certain conditions, a single leak can be responsible for a complete loss of refrigerant from the system. To satisfy the advocates we are now seeing the introduction of hybrid systems to overcome this issue.
Hydronic systems use less distribution energy although advocates of VRF systems point out that no circulators are needed to transfer refrigerant through a building BUT electrical energyis still required just to move refrigerant gas and liquid through the piping. That energy is supplied as electrical input to the units compressor. The electrical energy consumption for moving refrigerant through a VRF system, per unit of heat or cooling energy delivered, is significantly greater than that required for a well-designed Hydronic system!
Over the last few decades, highly successful refrigerants such as R-22 phased out due to their global warming potential. Replacement refrigerants have been and continue to be developed. The properties of these replacement refrigerants have compulsory changes in components such as refrigerant piping and the oils that are carried throughout the system with the refrigerant.
What refrigerants will remain acceptable over the future next years is impossible to know, however efforts to determine optimal future refrigerants will continue. This could lead to breakthroughs that allow refrigerants such as propane to emerge as the new standards. Eventually, VRF systems that rely on present day refrigerants could be rendered obsolete. The tubing that carries present day refrigerants throughout a building in a VRF system may not be suitable for future refrigerants or their associated oils. Upgrading a current VRF system could require replacement of piping, terminal units, as well as the costs of recycling refrigerant and oils. Such changes could be very costly.
Hydronic systems allow easy integration of thermal storage and Heating and cooling systems can benefit from thermal storage. The high heat capacity of water makes it an ideal thermal storage material for both heating and cooling systems. Heat pumps or chillers may produce the heated or chilled water at times when off-peak electric utility rates are in operation thus significantly reducing the cost of the delivered thermal energy.
Thermal storage of water can also be exploited in systems that have renewable energy heat sources such as solar thermal collectors, air-to-water heat pumps, or biomass-fuel boilers. Combined Heat and Power (CHP) systems also profit from water-based thermal storage.
The use of thermal storage for space heating and cooling with VRF systems is not practical. While Its possible to transfer heat from refrigerant to water using heat exchangers, it is not realisticto recover that heat back into refrigerant for successive distribution to VRF terminal units.
OUR FINAL ANALYSIS
Water remains the ‘pièce de résistance’in our opinion when it comes to moving thermal energy through buildings. Our business model from day one has been based on Hydronic systems that provide decades of reliable, safe, and the efficient delivery of heating or coolingbut of course its ‘horses for horses’
In the days where VRF is specified on over 60% of commercial UK projects, we remain the refreshing alternative, with traditional water based systems that are highly efficient, quick and easy to install, are very cost effective, perform and control in the same way without the need for expensive refrigerant based systems. There are now systems of hybrid VRF and hybrid chiller and heat pump which the analysis and comparisons we shall review another day…
This article is written by Simon Lamberton-Pine of DPAC UK Ltd
DPAC UK operate nationally through their network of agents and specifier’s,.
Why not get in touch to see if our technology can fit into your scheme. Or call us free on 0800 193 6288 to discuss your application.