Mechanical COMcheck enables us to maximize cost-effective energy efficiency at whichever level of priority is required by the building owner and/or relevant energy codes. It is invaluable when specifying heating and cooling equipment.
COMcheck may be used to generate a checklist of energy requirements that must be met during the design stages of buildings. While not mandatory, it is an invaluable tool that is accepted by state and local authorities.
COMcheck simplifies complex legislation. It was developed for the U.S. Department of Energy (DOE) in 1997 to make it easy for designers and builders to comply with residential high-rise and commercial building energy codes.
All design will be done as per International Energy Conservation Code (IECC).
The use of economizers, which are mechanical devices installed to reduce energy consumption, is required by ASHRAE Standard 90.1 in specified climatic regions with systems that have a cooling capacity of more than 90,000 Btu/h. Because efficiency benefits and cost-effectiveness can vary significantly depending on the climate, COMcheck has an economizer trade-off that enables building designers to use higher-efficiency air-conditioning equipment instead of an economizer.
Even though the trade-off is not specified in Standard 90.1, it was developed from data, in the form of tables, that are incorporated in the standard.
COMcheck provides energy efficiency ratio (EER) requirements for the economizer trade-off, indicating what increased cooling efficiency is required for a heat pump or air-conditioning unit to offset the absence of an air-side economizer in the climate zones where economizers are required. Depending on the equipment category size and zone the building is in, there will either be a 17% or 28% increase (or improvement) in the EER.
The trade-off is acceptable in most situations because it usually results in energy savings that are greater than the standard requires. However, it is not permitted for built-up systems because the supporting research for the trade-off applies specifically to unitary packaged equipment.
Load Calculations & Equipment Sizing
Load calculations are an essential element of all good mechanical design. Mechanical engineers use them when they select equipment to ensure that even when using the most economical items, comfort conditions will be maintained.
However, it is impossible to regulate the quality of assumptions made by designers or their judgment undertaking load calculations. The problem is that there are numerous variations on assumptions used when doing load calculations including the climate and future additions, as well as the designer’s experience.
Building inspectors don’t normally review load calculations for accuracy, which makes this a primary responsibility of the designer.
A similar scenario applies to equipment and system sizing, which, like load calculations is a vital element of good mechanical design. In addition to the availability and cost of equipment, there are a number of parameters that designers must consider, including sensible and latent loads, duct design, airflow, operating warm-up and cool-down sequences, and the location where equipment will be installed. While Standard 90.1 does take various parameters into account, in reality, there are so many possibilities, their requirements don’t have any practical effect on energy consumption.
Sizing requirements, like load calculations, aren’t explicitly enforced by building departments and local authorities. However, engineers have a legal responsibility to size and specify system equipment properly. Ultimately, the requirement is for systems and equipment to be specified correctly on the plans, and then, if necessary, a field inspector can do on-site inspections to ensure the system has been built in accordance with the approved plans.
Ventilation & Fan Power
If people are expected to remain in enclosed spaces for extended periods of time it is essential that these spaces are continuously vented with outdoor air. COMcheck refers to local codes for minimum ventilation requirements or to the International Mechanical Code (IMC).
When it comes to fan systems, COMcheck requires that they are operated continuously (when the space or room is occupied) to meet the provisions of the IMC. Additionally, a thermostat capable of being set to run continuously must be used, and systems must be capable of reducing the outdoor airflow to minimum levels using control dampers or fan volume controls either manually or automatically.
Another important element that COMcheck covers is the use of natural ventilation through windows, doors, louvers, and so on to ensure compliance. But users of the software are referred to local codes and the IMC for acceptable minimum opening areas that will ensure there are adequate natural ventilation rates.
The IMC allows natural ventilation to be used instead of continuous mechanical ventilation and it contains provisions that must be met if ventilation is provided via non-mechanical means. The IMC takes human response into account and allows occupants to ventilate spaces by opening windows and so on if they want to allow outdoor air into rooms. Acknowledging that they have the ability to control this type of ventilation, the IMC doesn’t expect it to be a permanent form of ventilation (in other words it doesn’t have to remain open all the time.)
While COMcheck does place limits on air handler design in variable flow systems, there are no limits on fan power in terms of W/cfm, which is how the efficacy of fans is measured. But this is simply because it was felt that the Standard 90.1 required couldn’t be enforced. Nevertheless, system designs that use the type of HVAC equipment allowed by COMcheck typically use less fan energy than the maximum allowed by Standard 90.1.
In terms of fan control technologies, COMcheck requires more efficient fan airflows that start at 25 hp rather than 75 hp required by the 90.1 code.