DOAS, Radiant Cooling

6 Reasons Why You Should Choose A DOAS Combined With Radiant Cooling For Your Next Project

There is a lot to consider when it comes to building design. Because of globalisation and fast paced technological advancement, building design is not just about being good, it is about being competitive and contemporary.

DOAS Project

That makes designing a new building, or even retrofitting an old one, difficult. Fortunately, when it comes to the HVAC system for your next project, there is a way to keep up with the times, and simultaneously deliver top-notch performance.


6 reasons why the HVAC system you choose for your next project should be a DOAS combined with radiant cooling


1. DOAS ventilates outdoor air, as the name suggests


DOAS are systems that ventilate 100 % fresh, outdoor air into the occupied space. This eliminates the problems associated with conventional systems that recirculate air. Recirculated air can transport contaminants, such as allergens or disease causing bacteria, through the occupied space.

Moreover, the ventilation of DOAS is done very accurately, using a lower flow rate and a reduced volume of air compared to conventional systems, such as variable air volume (VAV) systems. DOAS accomplish this while still meeting IAQ building code standards.

These features of DOAS ensure that they provide superior IAQ as well as ventilation compared to conventional systems.


2. DOAS provides better humidity control than conventional systems


DOAS decouple the handling of sensible (heat) and latent (moisture) energy. That feature, in addition to their reduced air flow rates and volumes compared to conventional systems, means they can deal with humidity control both more efficiently and more accurately and precisely than conventional systems. DOAS fitted with a desiccant or enthalpy wheel can control relative indoor humidity levels between 30 and 65 % (as recommended by IAQ building code standards such as ASHRAE standard 62.1), even in very hot, humid regions. Improved humidity control leads to improved IAQ, by controlling the growth and spread of microbes that cause allergic reactions, disease, or discomfort.

Notably, this excellent humidity control means that when DOAS are used in conjunction with a radiant cooling system, there are no problems with condensation. A common myth is that radiant cooling systems have problems associated with condensation build up, and therefore damage building materials or cause poor IAQ. “DOAS + Radiant” systems effectively control relative humidity so well that they eliminate any potential complications with condensation.


3. Radiant cooling provides better indoor environmental quality (IEQ)


Firstly, conventional systems that have large mechanical equipment for controlling temperature can create ambient noise that causes significant discomfort. Aural comfort is therefore improved by radiant cooling systems, because they are silent.

Secondly, conventional systems typically only monitor and control air temperature within the occupied space. However, the thermal comfort of occupants is determined by operative temperature. That means that to ensure the thermal comfort of occupants, one has to take into account energy exchange via conduction (direct contact with surfaces), convection (air temperature), radiation (energy transfer from nearby surfaces), as well as clothing and metabolic heat production. Radiant energy transfer is particularly important, as humans experience the operative temperature as more than 50 % mean radiative temperature (MRT). The more of these parameters a HVAC system regulates, the higher the comfort of the occupants.

Radiant cooling systems deal with radiant and convective energy transfer, which means that they provide much better regulation of thermal comfort than all-air systems.


4. Radiant cooling systems are easy to operate and maintain


Radiant cooling systems have a long lifespan, and very low maintenance requirements. All-air systems on the other hand require regular, costly maintenance to function correctly.

This difference in maintenance requirements is crucial, not only because of the difference in cost and effort, but because if the maintenance requirements of an all-air system are not met, IAQ will rapidly decline. This will then have negative consequences for the comfort, health, and safety of occupants.


5. “DOAS + Radiant” improves energy efficiency

Energy Efficiency Grade

It has been repeatedly shown over the last two decades that using a “DOAS + Radiant” system significantly improves energy efficiency compared to conventional systems. The savings range depending on the exact system configuration and the climate, but recent assessments have shown that a “DOAS + Radiant” system fitted with an enthalpy wheel can enhance energetic efficiency so considerably that it amounts to over 50 % energy savings compared to a conventional system.

As I have said previously in this blog series, energetic savings are not only important for meeting international standards for sustainability (and therefore combating the increasing threat of climate change), they are also good business. Energetically efficient HVAC systems massively reduce the operational costs of buildings, thereby increasing profit margins.


6. “DOAS + Radiant” takes up less space, at a lower initial cost


One of the biggest benefits of using a DOAS combined with a radiant cooling system is that the whole HVAC system takes up considerably less space than a conventional all-air system. This is because there is a large reduction in ducting, plenum space, vents, and mechanical hardware.

A reduction in the space required for the HVAC system has major benefits for building design. A “DOAS + Radiant” system allows for much more usable floor space, which frees up new opportunities for building design and space utilization. Furthermore, recent assessments of the first cost of a “DOAS + Radiant” systems have shown that the reduced material and building costs can actually lead to them being less expensive than conventional forced-air systems.




From these six points it is clear that “DOAS + Radiant” systems provide superior IEQ (IAQ and thermal comfort), greater efficiency, more space, and vitally, reduced first and running costs.

As a result, choosing a “DOAS + Radiant” system for your next project will allow you to provide excellent indoor conditions for occupants, while meeting requirements for trendy and sustainable design. Plus, importantly, it is the HVAC system that will cost you less and save you money.

Overall, choosing a DOAS combined with a radiant cooling system is the best option for competing on the global market in terms of occupant satisfaction, design, and profitability.



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