Monthly Archives: May 2014

New Scope for 2010

Scope

The scope of 90.1 changed in 2010. Before 2010, the Standard did not cover systems installed that were not for people comfort. Now the Standard includes systems installed for industrial or manufacturing processes. The scope now reads:

This standard provides:

  1. Minimum energy-efficient requirements for the design, construction, and a plan for operation and maintenance of:
  2. New buildings and their systems
  3. New portions of buildings and their systems
  4. New systems and equipment in existing buildings
  5. New equipment or building systems specifically identified in the standard that are part of industrial or manufacturing processes

First, notice that this Standard sets the minimum requirements for the worst energy efficient building built in a location that adopts the standard. The new addition to the scope is underlined. It allows us to identify an industry and set requirements for systems used in that industry. The Standard does not automatically cover the systems in industrial and manufacturing. We must first identify that industry. The Standard does automatically cover systems used for people comfort wherever they are found. We added computer rooms and data centers in 2010.

Opinions expressed here are solely my own and do not express the views or opinions of ASHRAE or the 90.1 committee.

 

New Purpose for 2010

Purpose

ASHRAE 90.1 Meeting90.1 Committee  Meeting

I have been involved with Standard 90.1 since 1999 and the 2010 edition contains the first change to the purpose of the Standard that I am aware of. Before this change, I could always tell people that 90.1 was a “permit” standard. It starts with design and ends with final inspection; ends with the building permit. That is no longer true. The Purpose now reads: “To establish the minimum energy efficiency requirements of buildings, other than low rise residential buildings for:

  1. design, construction, and a plan for operation and maintenance, and
  2. utilization of on-site, renewable energy resources.”

The new parts are underlined. The Standard now covers operations and maintenance for the life of the building. So, now the Standard is active for the life of the building. We did this because the energy savings that are present during the first year of operation reduces over time. We hope to add requirements for training and recommissioning of the building. We have added no operation and maintenance requirements to the Standard as of the 2013 edition. We are working on strategies to enforce any requirements we add, as most jurisdictions do not have inspectors that visit the building after construction ends. We also have not required the use of renewables in the Standard. It is now clear that we have the authority to set requirements for renewable equipment. We are working to make sure that there are standardized testing procedures for this equipment so that we can set minimum efficiency standards.

Opinions expressed here are solely my own and do not express the views or opinions of ASHRAE or the 90.1 committee.

 

Vestibule Requirement 5.4.3.4

Building Envelope

I just got off the phone with Greg McCall. He is an energy policy specialist with the City of Vancouver. We were discussing the vestibule requirements of section 5.4.3.4 in 2010 and addendum dm that changed the requirements for the 2013 standard.

As I travel around the country, I find that the wording of the exceptions to the vestibule requirements cause some trouble. Exception “e” excludes doors from having vestibules. The wording changed in 2013 in this way. “Building entrances in buildings that are: located in climate zone 3, that are less than four stories above grade, and less than 10,000 ft2 in gross conditioned floor area.” The words underlined were added and crossed out removed. The italics represent a word that is defined in the Standard; in this case, gross conditioned floor area, which can be found in section 3 of the standard under floor area.

Climate zone 3 is cooling dominated. This exception has a sister requirement, f, for more northern climate zones. “Building entrances in buildings that are: located in climate zone 4, 5, 6, 7, or 8 and that are less than 1,000 ft2 in gross conditioned floor area.” When I traveled to these climate zones, places such as Alaska, I was told that the 1,000 ft2 referred to the area for the entrance not the building. The changes in language are supposed to make it clear that it is the building that is less than 1,000 ft2. If you look at the definition of gross conditioned floor it certainly does make it clear. Greg is not so certain that the new wording will be understood. Many designers in northern climates have interpreted this to mean the door area has to be more than 1,000 ft2 before a vestibule is needed.

He also has a problem with exception g. “Doors that open directly from a space that is less than 3,000 ft2 in gross conditioned floor area and is separate from the building entrance.” This exception is for tenant spaces that might be on the ground floor of a large office building or hotel and open to the street. If these tenant spaces are less than 3,000 ft2 they do not need a vestibule. His question is , why do freestanding stores of 1,000 ft2 need a vestibule when these tenant spaces do not? Canadians like consistency.

Another change from the 2010 standard is for large buildings with entrance levels of greater than 40,000 ft2. The vestibules of these buildings, when the doors are self-closing, must have a travel distance between doors of 16 ft or more. The total area of a vestibule must be less than “50 ft2 or 2% of the gross conditioned floor area for that level of the building.”

Anytime you use 90.1, you need to check the definitions. As long as you understand what gross conditioned floor means, you can know that the exceptions are referring to the building and where you should put the vestibules. If you want to build the building in Vancouver, Greg can help you.

Opinions expressed here are solely my own and do not express the views or opinions of ASHRAE or the 90.1 committee.

 

VAV Box Control

HVAC

VAV boxes  VAV Box Control

I was working on a project for a client who owns many buildings. I put the new 90.1 2010 VAV box  control sequence on the plans and was told that it was not in their control standards. In 90.1-2013, this control sequence is required for systems using DDC controls, which covers almost every building these days. My client’s problem is that it is clear that if we speed up the air flow in heating, we will use more heat and not save energy. That is true as far as it goes, but the box does not set the space heating load; it just responds to it. If the hot air flow increases, it increases to keep the space comfortable.

The problem really starts with Archimedes, but the guys over at ASHRAE 62 noticed that when hot air is both supplied and returned from the ceiling, it tended not to fall into the breathing zone. If the outside air they are so worried about does not get to the people, it is not useful. They suggest that 20% extra outside air might fix the problem. If you do not want to add 20% more outside air, you are limited to a maximum supply temperature of 15°F above the thermostat design set point for heating.

When 90.1 looked at the situation, we took a little different approach. First, let’s think about VAV box operation. I am not from Archimedes’ time, but I do remember when we first started using VAV boxes. We had zero or 10% minimum sets and the boxes were good space temperature controllers. Now we default to a 30% minimum set and the boxes need reheat to control temperature. We have added a new control sequence to address this problem.

VAV

Let’s look at the new control diagram since we have it diagrammed here. As the space temperature drops, the box supply damper closes down to the minimum set. The supply air is normally around 55°F and so ,if the minimum set is 30%, it will continue to cool the space. The new sequence allows the minimum set to go down to 20% during the time the space needs neither heating or cooling. If we get lucky, there might be enough load in the space to hold the temperature steady at 20% airflow.

If we are not lucky, the hot water coil will open and we will be reheating the 55°F supply air. If we are reheating, how hot should we make the supply air? ASHRAE 62 says that the supply air from an overhead system cannot be more than 15°F above the room setpoint. It also says that the air has to be at traveling at 150FPM 4 foot above the floor.  If the room set point is 68°F, the supply will be a maximum of 83°F. 90.1 agrees that it is true that the hot air tends to hug the ceiling and short cycle to the return grille. So, if we make it too hot or buoyant (Archimedes), it does not mix with room air and will not heat the people. The air device that manufacturers give throw adjustment charts for air streams that are different temperatures than the room air. Looking at these, we thought we could stand a 20°F difference. This raises the allowed supply temperature from 83°F to 88°F.  At what temperature below body temperature will a person dressed for indoor winter conditions report a cold draft?

Here is what you have as a designer using the Standard 90.1 sequence we have had since 1999. You have selected a diffuser for the cooling airflow. Now it will be supplying 30% as much air as at design, plus you need to adjust the throw for buoyancy and still give the occupant a well mixed, comfortable temperature at chair level.

Remember that the heating load will be satisfied by CFM X delta-T X 1.085 (at sea level).  This is the same delta-T as the one we are working with, so ASHRAE 62 delta-T is 15°. Normally ,when we size the heating equipment, we calculate the room heating load without taking credit for internal loads such as lighting, people, or plug loads. This probably gives us the right load for prewarming the room before it is occupied, but this load may be high for the occupied space. The cooling load is calculated based on a 20°F delta-T. This means that, if the load was the same, cooling would use less air. A recent study of an office building found that 0.3 CFM per square foot would satisfy the occupants. This would be a 100% OA system if you were meeting ASHRAE 62 requirements.

We decided that you might need to speed the air up to 50% of design airflow to meet the heating load and throw the air to the floor. Now we are heating the 55°F air to 88°F for a 33°F air temperature rise, without reset. As the fan speeds up to meet the heating load, we will use more energy. That is why we are using the 20% minimum set for this sequence. This transitional low airflow will balance out against the higher heating airflow and generally save more energy than the old sequence. We think that the warm air delivered at the higher airflow will be enough for you to heat the space. You just have to sell it to your customer. I am still working on this problem and will keep you updated.

Opinions expressed here are solely my own and do not express the views or opinions of ASHRAE or the 90.1 committee.