Load calculation and system selection

Did you include thermal comfort charts for each type of space and each season similar to the one at: http://upload.wikimedia.org/wikipedia/commons/thumb/f/fe/Psychrometric_chart_-_PMV_method.pdf/page1-554px-Psychrometric_chart_-_PMV_method.pdf.jpg ? You can get the ASHRAE thermal comfort tool software for $117 at: https://www.ashrae.org/resources--publications/bookstore/thermal-comfort-tool or you can use a free online tool available at: http://www.cbe.berkeley.edu/comforttool/ I highly recommend downloading Google's free Chrome web browser and using it if you are going to try using the Berkeley free online tool. You can get Google Chrome at: www.google.com/chrome/‎ That would cover the part about whether all design conditions fall within the ASHRAE 55-2004 acceptable ranges. As far as whether the design HVAC system is capable of meeting these setpoints, I'm not sure exactly what the reviewer is looking for. Perhaps they would like to see process psychrometric charts similar to the one in the Documentation Toolkit tab of this LEEDuser, but I've never had to do that for this credit. Maybe a narrative describing the capacity and behavior of the actual HVAC system at various full load and part load conditions would suffice. Include a description of how the HVAC system meets both the temperature and humidity setpoints at full load cooling, full load heating, part load cooling, and part load heating, in order to include comfort conditions for all seasons in your narrative.

You should also provide a written narrative describing how the system reacts in full load, medium part load, and also on the coldest design day. I would use the coldest design day for "winter" and somewhere between that and full load for "fall" and "spring". Also be sure to include information for each space type at each of the full load and part load conditions analyzed, showing the range of acceptable temperature versus humidity comfort conditions for the clo level of the occupants, met level of the occupants, and air speed, with your setpoints or expected conditions for the various load conditions shown as falling within those comfort ranges. If it gets a little chilly at times even though heating is not needed, you could use a higher clo level for that time of year if people would often wear a bit more clothing at that time.

That sounds reasonable except that 50 zones is probably too many to describe individually. You should just analyze each different kind or type of space, not every zone. For example, office areas, meeting rooms, lobbies, etc. whichever types of spaces you have in your building. If you have 10 different office zones, just deal with that type of space once, not 10 different times. The important things to focus on are: 1. Show that the conditions in each type of space with its own type of activity fall within the ASHRAE 55 comfort range for each season. You can do this with the comfort tool report, as you say in number 1 above. 2. Convince the reviewer in words that your combination of weather conditions, building characteristics, and HVAC systems will keep not only temperature but also humidity in the comfort range at part load conditions ("spring, fall, winter") as well as at full load conditions. A description in words may be more effective at doing this than numerical reports on 50 different zones would be.

Here's what I wrote in response to a review comment on an NC version 2.2 project. The credit was awarded. The details of the question were different than in your case, but similar in that the reviewer needed to know that comfort conditions would be maintained for all design and part load conditions. "The reviewer has requested further information on the operation of the 2-pipe system and how it is designed to react to rapidly changing climate conditions in intermediate seasons. The reviewer has further requested clairification on the operation of the heating only loop specifically how the 148 degree water running thru the cabinet heaters and the radiant floor will not cause the building to over heat. The following narrative is provided to help clarify these issues: 1. Two Pipe system: Active conditioning is used in all spaces. Winter and summer design criteria fall within the standard 55 envelope. Spring and Summer criteria fall within the combined winter and summer envelopes. The dual temperature hot/chilled water system is isolated from the area chilled water and hot water loops by heat exchangers. One heat exchanger is dedicated to heating and the other to cooling. The dual temperature system serves only the [6,000 square foot new wing], limiting the volume of water in the loop. When the dual temperature loop is in heating mode, the chilled water heat exchanger is isolated and vice versa. In heating mode, the hot water supply temperature in the dual temp loop is reset from 150 to 100 deg F as the outdoor temperature varies from 10 to 60 F. Automatic change over between the heating exchanger and the cooling exchanger is provided by the DDC controls based on outdoor air temperature.The DDC control system will automatically change the system from heating to cooling, and the air systems all have economizer controls. 2. Heating Only Loop The area heating loop serves the vestibule heaters and the radiant floor. The radiant floor system has its own circulating pump and a 3-way valve to allow mixing radiant floor return water into the radiant floor supply water, for independent temperature control of the radiant heating loop water. In addition, the zones served by the radiant loop are automatically shut off by control valves when the thermostat in the zone is not calling for heat. The vestibule heaters cycle two-position control valves and fans based on the DDC sensor in the space.The water temperature to the heating loop is also reset based on outdoor air temperature and is only at 148 degrees when the oudoor air temp is at 0 degrees."

The narrative looks very good. I have two suggestions that would strengthen it, if they apply to your VRF system. I believe some VRF units automatically vary fan speed as well as supply air temperature. If this is true of your units, stating that fact will strengthen the case that they will dehumidify well due to the latent/moisture portion of the heat removed by a cooling coil increasing as airflow decreases. In addition, some VRF thermostats have an option to choose "dry" mode. That could be another help in assuring good dehumidification is available, if your VRF thermostats have a dehumidification mode option that can be selected by the occupants. Here's part of what I wrote on a VRF heat pump project in response to a similar review comment on a version 2.2 project. The credit was awarded. "Humidity Levels During Periods of Low Cooling Load -- Latent cooling (dehumidification) during periods of varying cooling loads is addressed by: 1) a "dry" setting on the individual indoor heat pump fan unit occupant-adjustable thermostats, which reduces sensible capacity and increases latent capacity, 2) latent heat exchange between exhaust air and incoming outdoor ventilation air in the energy recovery ventilation system, and 3) tempering cooling/heating coils in the mechanical ventilation supply ductwork. These features, when combined with internal sensible heat gain, provide the ability to reduce total moisture levels and relative humidity even under conditions of low sensible cooling load."