DOAS, HVAC Systems, Radiant Cooling

How A DOAS Combined with Radiant Cooling Can Solve Your HVAC Problems

Problems with your HVAC system can manifest in a range of ways, all of which are worthy of concern. Whether the problems are financial or comfort related, they need to be dealt with.

Fortunately, comprehensive research has shown that a DOAS combined with radiant cooling can help resolve your HVAC issues.

There are four main categories of problems with HVAC systems, each are listed, along with why a “DOAS + Radiant” can help solve them:


1. Indoor Environmental Quality (IEQ) problems


The best place to start is with the problems with the service that HVAC systems provide. An HVAC systems’ primary function is to regulate the indoor environment, thereby keeping you comfortable, healthy and safe. If your HVAC system is giving problems here, they will be immediately noticeable. Problems with IEQ caused by the HVAC system can come from poor regulation of the thermal environment, poor regulation of indoor air quality (IAQ), and noisy mechanical components.

Thermal comfort: 

Conventional all-air systems only monitor and regulate the air temperature. However, the thermal comfort of occupants is dependent on the operative temperature. Operative temperature takes into account all pathways of sensible (heat) energy transfer, and humans perceive operative temperature as over 50 % the mean radiant temperature (MRT). DOAS combined with radiant cooling helps solve this problem by

monitoring and regulating not only the air temperature but also the MRT. This greatly improves the occupant’s perceived thermal comfort levels.


doas combined with radiant cooling

Conventional HVAC systems, such as variable air volume (VAV) systems, have several problems with IAQ. Firstly, these systems typically recirculate air to save energy. Recirculating air can transfer contaminants such as allergens or disease-causing bacteria between occupants, significantly reducing IAQ. Secondly,

systems such as VAV often struggle to provide adequate ventilation to the occupied space. This may reduce IAQ, and perceived comfort. Thirdly, conventional systems have a single air handling unit (AHU) to control ventilation rate, as well as humidity and temperature control. This means that prioritizing one can compromise another. DOAS combined with radiant cooling solves these problems by providing 100 % fresh, outdoor air directly to the occupied space. This reduces the issues associated with recirculation, as well as with improper ventilation. Moreover, because DOAS systems decouple the handling of sensible and latent (moisture) energy, they do not have the problem of comprising ventilation rates to maintain temperature and humidity control. In fact, DOAS can achieve ventilation rates that meet international building code standards with both a reduced air flow rate, as well as a lowered air volume. This further improves comfort and energy efficiency. Combined, these features of a “DOAS + Radiant” system serve to provide superior IAQ (and therefore, IEQ) compared to conventional VAV or other forced-air systems.

Aural comfort

doas Aural comfort

The problem here is that conventional all-air systems often have mechanical equipment installed at crucial points in the duct system to control ventilation and air temperature. These mechanical components can be noisy, which can be distracting or annoying, thereby lowering the IEQ. “DOAS + Radiant” systems eliminate this problem because they provide more precisely and accurately controlled ventilation at lower volumes and flow rates. More importantly, radiant cooling is completely silent. Therefore, a “DOAS + Radiant” system will lower ambient noise significantly compared to conventional systems, thus improving aural comfort and overall IEQ.


Tight control


The final problem with IEQ that conventional systems have is that they are often incapable of controlling IEQ parameters under difficult conditions (such as high outdoor temperature and humidity). This is not only a problem for IEQ, but also for meeting legislative requirements; generally, building codes for IAQ list not

only requirements for the maximum concentration of contaminants in the air but also the ventilation rate. As mentioned above, for conventional systems to meet ventilation requirements, they often have to forego properly regulating temperature or relative humidity. This issue can be solved by “DOAS + Radiant” systems through the decoupling of energy handling. Separate control of temperature and relative humidity allow both to be controlled more precisely, accurately, and efficiently. That means that “DOAS + Radiant” will be able to provide ventilation rates that meet building code standards while maintaining operative temperature and relative humidity within the desired range that maximizes comfort.


2. Difficult maintenance


All-air systems can have vast networks of ducting, as well as large plenum space. Moreover, HVAC systemsthat recirculate a lot of air require high-quality filters to minimize the recirculation of contaminants. Combined, these features create a high maintenance demand. Filters have to be frequently cleaned or

replaced, and the ducting must be cleaned regularly to avoid dust or mold build up. Falling behind on maintenance for these systems can be highly costly, as poor maintenance will cause a decline in IAQ, which lowers comfort, and can cause discomfort or health issues. “DOAS + Radiant” systems greatly reduce the space and size of the duct network and do not recirculate air. This reduces both the amount and frequency of cleaning needed. Combined with the minimal maintenance requirements of a radiant cooling system,

“DOAS + Radiant” therefore serve to cut down on the frequency, effort, and cost of maintenance.

3. Poor energy efficiency

Energy Efficiency

In the context of climate change, and increasing pressure to improve profitability, energy efficiency has become a hot topic. That means that one of the concerns that your HVAC system might be giving you is that it is using too much energy. This worry can be solved by a DOAS combined with a radiant cooling system. Studies have shown that “DOAS + Radiant” systems significantly increase energy efficiency compared to traditional systems. The figures for the actual energy savings have varied widely depending on some factors, including the climate, system configuration, and size of the project. However, saving accrued by contemporary systems are estimated to be over 50 % compared to conventional HVAC systems.

4. High running costs


The final problem you may be having with your HVAC system is that it simply costs you too much. This follows from the previous two points. Essentially, high maintenance requirements and energy usage associated with conventional all-air or forced-air systems can lead to high running costs.

As explained above, “DOAS + Radiant” systems considerably improve energetic efficiency and reduce maintenance costs. Together, these mean that “DOAS + Radiant” systems can drastically decrease building costs over time. These systems can pay back the cost of installation within a year, and after that begin

saving money compared to conventional systems. Also, as I have explained previously, the improved IEQ afforded by “DOAS + Radiant” systems will eliminate ‘sick building syndrome,’ therefore massively reducing the costs of absenteeism and illness, and increasing the productiveness of workers.




A poorly functioning HVAC system can cause more problems than it solves. These are no small problems either; poor IEQ, IAQ or high running costs can cripple profitability, cause health issues and affect workplace efficiency. Using a ‘DOAS and Radiant’ system can help resolve these issues.



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