Q: What is a zone? What is a system? Are zones independent of systems?

A: In Rhvac Online, a zone is a group of one or more rooms. Zones are convenient when you want to obtain separate loads for different areas (zones) in a building. You are not required to zone your building and by default there is only one zone. A system is a group of zones maintained under certain design conditions. System design conditions are common for all zones in a system and include inside temperature, infiltration rate, ventilation, etc. The Rhvac Online program allows you to have several systems within the same project and specify different design conditions for each one of them on System Data page. You can assign a zone and a system for every room in your project (see Room Data topic). You can also obtain load reports for every system and zone in your project (see the Select Reports topic). Because Rhvac Online groups rooms into zones and zones into systems, zones, as well as rooms, are not independent of systems to which they are assigned. For example, zone 1 of system 1 is not the same as zone 1 of system 2.

Q: What is the purpose of the Default room and why the Default Room Data page is different than the Room Data page?

A: The Default room stores your most used material types and data entries. The Default room is not a real room and its presence does not affect cooling and heating loads. It is provided for your convenience, so that, instead of entering the same room component over and over again, you could simply copy it from the Default room. The information on the Default Room Data page does not have to be filled out and your input is not checked for errors (hence the absence of Evaluate button on the Default Room Data page as opposed to the Room Data page). For more information on how to use the Default room see Default Room Data and Room Data topics.

Q: What roof material code should be selected for a roof with a ceiling underneath an attic?

A: The 18A through 18F roof + ceiling material selections should be the appropriate choices.

Q: How do I handle an attic with the outside air at 95 F, inside air at 75 F, and the attic air at 125+ F?

A: Temperature differences between the attic air and the outside air are built into the HTM values for roof+ceiling material types. All you have to do is to choose your roof+ceiling material type (18A through 18F) in the roof material drop down box on the Room Data page.

Q: How do I handle an inclined roof? What if the roof only has one slope?

A: If the roof is exposed to a conditioned area, select Roof on Exposed Beams roof material (selections 17A through 17L) and enter dimensions of inclined and flat portions of the roof in the Room Data page. If the roof is not exposed to a conditioned area, such as in the case when there is an attic, choose an appropriate roof+ceiling combination for the roof material and specify dimensions of the ceiling only.

Q: What are the limits of the demo version of Rhvac Online?

A: The load calculation demo version is limited to three rooms, 15' wall lengths and 8' wall heights. The duct design demo is limited to 6 trunks and 6 runouts per project. The Manual S Calculator online demo is limited to 19,000 Btuh capacity. The demo version will perform the same calculations, use the same databases, and allow the same data entry procedures as the full version of Rhvac Online. If you like the demo version you can upgrade to the full version. The full version will allow access to the program's maximum of 999 rooms divided among a maximum of 30 systems and 50 zones per system. Call Elite Software at 1-800-648-9523 or 979-690-9420, or visit www.elitesoft.com for more information.

Q: Why doesn't the supply CFM work out to 400 CFM per ton for my project?

A: 400 CFM per ton is just a rule of thumb. Remember that the supply CFM is based on the leaving coil - room delta T (temperature difference) and the sensible load in the space. Check to make sure that this delta T is 20F or very near 20F. Also, if the latent loads are a high percentage of the total loads, the supply CFM will calculate out less than 400 CFM per ton even with a 20F delta T. 400 CFM per ton is not a hard and fast rule and the supply CFM for any project can work out higher or lower than 400 CFM per ton.

Q: Why does changing the direction of a roof not affect the roof's loads?

A: The direction of a roof is meaningful only if the roof has a skylight window(s). Unless the roof is referenced by a skylight window(s) in Glass entries on the Room Data page, the direction of the roof will always be UP, no matter what direction you specify and, therefore, will not affect the loads.

Q: I entered a ventilation value in the Room Data screen, but my results don't show this ventilation. Why not?

A: Rhvac Online uses ventilation entered for a given system in the calculations. You must enter this value in the HVAC System Data screen. The Ventilation Required CFM entry in the Room Data screen is just used as a check for your benefit in the printout to ensure that individual room ventilation requirements are met by the system.

Q: What's the difference between ASHRAE and ACCA Manual J?

A: ACCA Manual J is a residential load calculation procedure that makes many simplifying assumptions so that it is reasonably easy to perform manual heat gain and heat loss calculations. ASHRAE has both a residential and a commercial load calculation method. The ASHRAE residential load calc method is little used and thus any mention of ASHRAE load calc methods are nearly always assumed to be for commercial purposes.

ASHRAE actually supports numerous commercial load calculation methods with acronyms like TETD, CLTD, TFM, RTS, and HB. All of these methods employ more sophisticated procedures than what Manual J uses. Perhaps the greatest difference between Manual J and ASHRAE procedures involves time of day. ASHRAE has a different load factor for every hour of the cooling design day. Walls, roofs, and glass sections each have their own hourly load factors that are dependent primarily on orientation and time of day.

In Manual J, east glass has one summer load factor. Nevermind that east glass has more heat gain in the morning and less heat gain in the afternoon. The one load factor averages the varying heat gain during the day for that orientation. East and west glass have the same load factors while north and south glass are each unique. Wall loads are even further simplified in Manual J. Not only is time of day not a variable, but orientation also has no effect on the summer heat gain for a wall. Thus, a north wall receives the same load factor as a south wall.

Rhvac Online is based on Manual J and is intended primarily for detached residential buildings. Some HVAC professionals make their own judgement about whether a building used for commercial purposes can be treated like a residence. After all, you can occasionally find a regular house converted for use as a beauty salon for example. Elite leaves such decisions to the judgement of the designer, but cautions that Manual J tends to calculate lower cooling loads than ASHRAE, especially for glass. Typical glass cooling load differences might be 20% to 40% higher for ASHRAE as compared to Manual J.

Elite Software's CHVAC program is based on the ASHRAE CLTD method. Thus, it is appropriate for all commercial applications. But what about using an ASHRAE commercial load method on a residential structure? Many consulting engineers use ASHRAE commercial procedures for load calculations on custom homes. As mentioned before, ASHRAE loads will always be higher than the loads calculated using Manual J. Some designers feel like ASHRAE commercial methods overstate the loads on a residential structure. Each designer has to make their own decision on whether a particular method is appropriate for use on their specific project.

Q: Where can I get expanded ratings data for HVAC equipment?

A: Go to the following page: https://www.elitesoft.com/web/equipmentperformancedata/equipmentperformancedata.html

Q: Calculated loads seem to be too low. Why?

A: There are several factors that can greatly contribute to the loads on a building. Some of the main items are building dimensions, infiltrations, people, and "hidden" sensible and latent loads. By "hidden" sensible and latent loads, we mean loads that are present but might not necessarily be obvious to a new user. Latent loads from bathrooms and sensible equipment loads from televisions are two such examples.

There are several things that you should check and that might be responsible for low loads:

Check your component dimensions for each room on the Room Data page and check that they have been entered using the right units. For example, you may have your window dimensions written down in inches, but you need to enter them into Rhvac Online in feet.

Check the infiltration rate entered on the System Data page and make sure it is not too low. You should rate your buildings conservatively on their construction. By conservatively, we mean be critical about rating a house as having "tight" construction. If there is any doubt as to the "tightness" of the construction on a building, select your infiltration value somewhat on the high side.

Check your people loads entered on the Outdoor Design Conditions page and make sure that reasonable values have been entered for active and inactive loads per person. Next, make sure that you have enough people in the building. You can enter the number of people present in each room on that room's Room Data page. A recommended minimum amount of people is two people per every bedroom.The important point to remember is that Rhvac Online does not depend on the time of day, rather it depends on the peak load. Therefore, you need to place the people where you expect them to be when the peak load occurs. Finally, the two people per bedroom is a recommended procedure to estimate the minimum number of people in a building. If your clients entertain guests quite often, you would like to have their HVAC system sized so that your clients and their guests will be comfortable. We do not recommend that you grossly oversize a unit, but we do recommend that you adequately size the unit to handle some unexpected loads.

Check your sensible and latent loads. The load adjustment can be made for each room on that room's Room Data page. Some loads may be "hidden" to the new user. For example, appliances produce a sensible load. Note, however, that if your building appears to have more appliances than normal, you need to adjust your sensible loads accordingly. Another "hidden" load is bathrooms and washrooms. These rooms contain heated water and, thus, usually produce a latent load. We recommend that you add 500 Btuh for each bathroom and washroom.

Q: Calculated loads seem to be too high. Why?

A: The first place you should look when the loads seem excessive to you is the infiltration rate entered on the System Data & Load Preview tab of the System Data page. An excessive infiltration rate often occurs when the building is in excess of 3000 square feet. Even though Manual J recommends using the same infiltration rate for all buildings over 2100 square feet, we have found that you should continue reducing the air changes per hour rate as the building size increases over 3000 square feet. Another reason for excessively high loads could be windows. Remember that windows are entered in units of feet, not inches.

Q: Why does the sum of the room airflows not equal the airflow of the system?

A: It is sometimes normal for the sum of the room airflows to not equal to that of the system, and does not necessarily indicate you have done anything wrong. One way that can happen is if the Airflow Option input on the System Data page is set to "Room" instead of "System." That means the room airflows are set to equal the larger of the airflow needed for the winter or summer. Since the ratio of a room's sensible gain to the sensible gain of the system is probably not equal to the ratio of the rooms sensible loss to the sensible loss of the system, the rooms' heating and cooling airflows are probably different, so the sum of the room airflows may not equal that of the system.

Another way it can happen is when you have assigned rooms within the same system to more than one zone, and the "Use CV if multizone" input on the System Data page is set to "No." When that is the case the program will use the peak fenestration gain procedure to determine the sensible gain of windows and skylights at the room level. The sensible gain for windows and skylights at the room level (and therefore room airflow) will then be equal to the sensible gain of the hour in which the glass sensible gain is the highest. Since the sensible gain for windows and skylights at the system level is always based on the average load procedure plus any AED excursion load, the sum of the room cooling airflows will be larger than that of the system in this case.

When neither of the above two situations is occurring and you have draw ductwork using the graphic Manual D Ductsize component in Drawing Board, it is still possible for the sum of runout airflows for a system to not equal the airflow of the supply main trunk, which may indicate that there is a problem. If you have set the Airflow Unlinked property to True for any supply runout in the system, its Flow Discharge property is then user defined, and therefore may not be equal to the airflow calculated for the room. This discrepancy can also occur if you have any rooms in the system in which you have not placed a supply runout object, or if you have attached a supply runout for a room to a duct system that is not the same as the System Number property that you assigned to that room.

Q: How do I obtain a specific desired Summer Grains Difference Value?

A: The summer grains difference value shown in the general project report is not a user input value. It is a value that Rhvac Online automatically calculates based on the grains value of the indoor room condition and the grains value of the outdoor design condition.

Q: Why do the reports do not show net tons or recommended tons?

A: Showing net and recommended tonnage values on the reports is optional. Click "File | Select Reports", and check or uncheck the boxes, "Show Net tonnage" and "Show Recommended tonnage".

Frequently Asked Questions About Rhvac Online

Frequently Asked Questions About Rhvac Online

Check your component dimensions for each room on the Room Data page and check that they have been entered using the right units. For example, you may have your window dimensions written down in inches, but you need to enter them into Rhvac Online in feet.