2019 ASHRAE BPAC – Preconference Workshops

2019 ASHRAE BPAC - Preconference workshops

2019 ASHRAE Building Performance Analysis Conference - Preconference Workshops

Effective simulation throughout the building life cycle with Tas (presented by EDSL)

On Tuesday morning, we held a pre-conference workshop with attendees from high performance building design teams, firm leaders, energy analysts, and other related backgrounds.  Michael Sawford and Robert Yori reviewed how Tas can be used throughout the ASHRAE 209 cycles.  This included a general introduction to Tas, BIM and BEM interoperability workflows, and whole building simulation using Tas Systems – our component based tool for simulating innovative and advanced plant room and air-side systems. 
 
The workshop included live simulations of projects, systems inspection using Tas Systems, and a case study of a post occupancy performance analysis. To wrap up, attendees stayed for lunch and were joined by our afternoon workshop participants for some networking and knowledge sharing.  

Crafting your story with building performance simulation data (sponsored by EDSL)

The afternoon workshop was well attended with some last minute sign-ups taking the total to 23. 4 attendees from our morning workshop also joined us for the afternoon which turned out to be a great workshop led by Alejandra Menchaca (Thornton Tomasetti), Kjell Anderson (LMN Architects) and Aman Singhvi (AECOM).

2019 ASHRAE Building Performance Analysis Conference

2019 ASHRAE Building Performance Analysis Conference

2019 ASHRAE Building Performance Analysis Conference

EDSL were once again pleased to sponsor 2019’s ASHRAE BPAC event, which was held in Denver last month.   Many thanks to everyone who attended our workshops, stopped by our table, and took a few minutes to chat with us about Tas.  In comparison with last year’s ASHRAE/ IBPSA joint meeting, our conversations trended more toward Tas’ functionality and its capabilities, while last year we spent a lot of time introducing Tas to people.  It’s rewarding to see that Tas is increasingly recognized and being used in North America.

In addition to our outreach about Tas, EDSL was involved in a number of the program sessions throughout the week.  We proudly contributed to Amir Rezaei’s “Geometry Translation – the Good, the Bad, and The Ugly” session, offering our thoughts and experiences with BIM to BEM, what’s working, and what would be improved upon.  We were also given the opportunity to opine on the state of software and energy modeling in the Vendor Town Hall, where we touched on Tas’ robustness, speed, and accessibility.  
 
EDSL also continued our active participation through Project StaSIO’s third year and 2nd annual competition, helping to organize this year’s competition, manage the jury selection, and improve the website.  And we’re not finished yet – as a result of this year’s outstanding entries, we have some new ideas in store for next year’s competition.  So stay tuned!

BuildingEnergy NYC 2019

EDSL USA at BuildingEnergy NYC 2019

EDSL at NESEA’s BuildingEnergy NYC Conference + Trade Show in September, held in downtown Manhattan.
 
This was our second opportunity to be involved with NESEA, and we were glad to be involved once again in the community by sponsoring BuildingEnergy NYC.  Being in EDSL USA’s home city, it was the perfect opportunity to announce our Tas Workshops.  Throughout the week of October 21 we will be hosting a series of workshops that introduce Tas, including both general and deeper-dive sessions.

We hope that many of the BuildingEnergy NYC attendees will be able to join us along with other building performance analysts and educators in building science from in and around the New York area.  There are still some seats available, so register now if you’d like to join us.

2019 ASHRAE Building Performance Analysis Conference & Project StaSIO

2019 ASHRAE Building Performance Analysis Conference and Project StaSIO

After a tremendously successful first year of IBPSA-USA’s Project StaSIO, EDSL USA VP Michael Sawford is looking forward to expanding its reach and offering.  “Last September’s Building Performance Analysis Conference and SimBuild was the perfect opportunity to introduce Project StaSIO to the world, and the competition provided a great way to kick start the resource for the BEM community.

This year promises some exciting advancements – new leaders have joined, enabling the committee to expand its range and potential impact. Thanks in large part to the DOE, who funded the initiative, we are redeveloping our online presence, and refreshing the website to create an engaging, valuable, easy-to-use resource for inspiration and research. 

2019 ASHRAE Building Performance Analysis Conference - Pre-conference Workshops

In addition to our involvement on the StaSIO committee, EDSL is supporting the initiative and its goals in several other ways. At ASHRAE BPAC 2019, we are sponsoring the pre-conference course Crafting your story with building performance simulation data, led by experts from Thornton Tomasetti and LMN Architects.  We will also be running a pre-conference course entitled Effective simulation throughout the building life cycle with Tas”.  Both worships will take place on Tuesday, September 24.  

You can learn more and register here, spaces are limited so please register early:

 https://www.ashrae.org/conferences/topical-conferences/2019-ashrae-building-performance-analysis-conference 

DOE BTO Peer Review 2019

US Department of Energy's Building Technologies Office BEM Peer Review 2019

Along with other industry leaders and stakeholders, EDSL’s Michael Sawford was invited as a reviewer for the DOE’s BTO BEM Peer Review. The review took place April 16th last month, where participants were asked to review and advise the current range of BTO projects with the goal of furthering research and the advancement of building simulation in the design, operations, and maintenance of buildings.

BTO's Request for Information

The Building Technologies Office has produced a request for information and provided all the necessary information on the EERE exchange website for the wider BEM community to get involved and participate. IBPSA-USA has also provided a useful survey for the community to get involved and respond to the RFI.
 
Responses to this RFI must be submitted electronically to BTO_BEM_RDO@ee.doe.gov no later than 5:00pm (ET) on June 3, 2019.
 
To participate follow the links below:
  •  
  • DOE Resources:
  • IBPSA-USA resources for participating:

Tas two-way link to EnergyPlus

See the About Tas page to learn more about how we are working on improved flexibility and interoperability with Tas and EnergyPlus/eQuest to support the BEM community:
 

SimAUD 2019

EDSL USA at SimAUD 2019

EDSL was at SimAUD 2019, the symposium on simulation for architecture and urban design.
 
This was EDSL’s first SimAUD event.
 
Working with professionals, researchers, and students in the fields of architecture, engineering, and sustainability sends a strong message about the power and effectiveness of transdisciplinary collaboration, analysis, and simulation.” said Michael Sawford, Vice President of EDSL USA.
 
Here are a few items we found of particular interest:
  • Interoperability remains a sticking point in transdisciplinary collaboration workflows.  One of EDSL’s objectives is to minimize barriers across tools and support informational continuity.  Each discipline can work with their best-suited applications while also being able to communicate upstream and downstream with their peers.  To this end, Tas software supports two-way interoperability with EnergyPlus -based tools, and the ability to import eQuest model data.  
  • Parametric optimization is always a popular topic at research conferences, and Tas currently supports LBNL’s GenOpt tool for multiobjective optimizations.   Thanks to the conference presentations and feedback, we are now researching additional optimization algorithms for enhanced flexibility.  
  • A number of presentations focused on reducing simulation times through model abstraction and reducing the number of simulations required.  Tas software can deliver results more quickly thanks to its own fast and robust simulation engine, allowing users to explore the same size design space more quickly, or a larger design space in the same amount of time.  Coupled with the strategies presented could lead to even quicker results.
EDSL Tas table 1
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TasGenOpt – Parametric Multi-objective Optimisation analysis in Tas (below: 23 simulations in 7 minutes):

EDSL's Tas software at Georgia Tech

Georgia Tech was an ideal venue for SimAUD, thanks in particular to their innovative school of architecture led by Scott Marble.  Dr Dennis Shelden, head of the Digital Building Lab, gave a thoughtful overview of simulation and technology’s trajectory through the past thirty years, and Dr Fried Augenbroe wowed us with an inspirational collection of his reflections about building simulation and its effectiveness.  
 
We are especially proud that EDSL’s Tas software is being taught in Dr Augenbroe’s High Performance Building Lab, and are working with the Lab on the Living Building Challenge certification for the new Kendeda Building for Innovative Sustainable Design.  

BuildingEnergy Boston 2019

EDSL USA at BuildingEnergy Boston 2019

EDSL was at NESEA’s BuildingEnergy Boston Conference + Trade Show, it’s been a full week and we are finally getting caught up.

As this was EDSL’s first NESEA event, we weren’t sure what to expect. The organization was great and we were welcomed by the community. We had hoped to attend more classes but thanks to interest at the booth we were afforded little time. It was encouraging to see the diversity of attendees ranging from policy makers, product manufacturers, architects, engineers, and everything in between. The culmination of many discussions with people from diverse backgrounds lead to possibilities for the use of our software in traditional applications and in new directions.

We are very excited to participate in BuildingEnergy New York as it is our home base in the US. We are hoping to build a strong local user group and are looking forward to being involved in the NESEA community going forward.

exhibit 2

Energy, CO2, and Embodied Carbon - how the AEC industry can turn buildings into carbon sinks

Michelle Apigian (ICON Arcitecture) and James Petersen (Petersen Engineering) opened the Keynote session ‘Carbon Drawdown Now! Turning Buildings into Carbon Sinks‘ presented by Chris Magwood (Endeavour Centre), Ace McArleton & Jacob Racusin (New Frameworks). The keynote focussed on how buildings have the potential to become the world’s fifth largest carbon sink, rather than a leading emitter and how the work of the AEC industry is essential for climate justice and social equity.

Free Tas academic licenses

Academic Announcement

EDSL Tas - Free Academic Licenses

EDSL is committed to supporting the academic community and expanding the opportunities available to students and faculty alike. As such, we are pleased to announce that we offer Universities our Tas Engineering thermal dynamic simulation software free of charge to instructors and students. To further support instructors, EDSL will also offer no-cost training and support for course lecturers and teaching assistants.

Academic programs involving environmental or mechanical engineering, architecture, sustainability, building services, or another related field can benefit from Tas Engineering.   It simulates an array of environmental and systems design factors including daylight, natural ventilation, HVAC systems, and climate based daylight modeling. 

Tas in the Classroom

Tas is well suited for learning.  Students and teachers can focus less on working around software limitations and more on describing designs, systems, and their components easily, accurately, and clearly.

With the ability to generate and simulate models quickly and easily, it reduces the friction typically associated with preparing geometry and other data for simulation.

The Results Viewer tool combines and displays results in an integrated environment, making it easier to understand relationships among multiple design factors and their ramifications.

It supports highly granular data input and output, enabling students to investigate thoroughly, and minimizes any ‘blackbox’ circumstances in which assumptions and methodologies are not clearly understood.

The fully-featured Systems module combines diagrammatic-level equipment and system definition with the full flexibility of a component-based design tool.

An array of ASHRAE, COMNET, and NCM(UK) database resources are included, containing constructions, calendars, internal conditions, and weather files.  Together, they serve as an extensible library of components and conditions for students to utilize confidently.  Custom resources can be created for more focused areas of study.

Testimonials

Testimonials from early-adopter students and graduates with backgrounds in Mechanical Engineering and Building Performance

“Tas Engineering software is a great platform for students to explore the world of simulation of buildings and further enhance their building physics knowledge along with understanding the simulation outputs generated.”

“During my curriculum for 2 years at University, I have been exposed to various simulation software packages, which all had different user interfaces and calculation methods. The interface that Tas Engineering provides is very user friendly and as a student it was one of the easiest softwares for me to learn.”

“All modules had in-built tutorial videos which makes it easier for me to troubleshoot problems.”

“I first used Tas when I started my career in the HVAC industry. The Systems module was a great way for me to learn how components are arranged in a system and how they all interact with each other. Creating schematic layouts with custom systems in Tas was a great learning tool and it helped further my understanding of different system types and arrangements.”

“As a student, I would strongly recommend young individuals to use Tas Engineering and enhance their skills.”

Terms and Conditions

The software is to be used for educational purposes only, commercial use will require a paid license.

Typical educational license duration is one semester, and maximum duration is one year.  Alternative terms will be considered on a case-by-case basis.  Licenses are renewable upon request with verified academic credentials.

Instructor-assisted training will be provided at no cost to lecturer(s) and/or teaching assistants of courses relating to environmental or mechanical engineering, architecture, sustainability, building services, or another related field.  Lecturers and/or TAs will be responsible for supporting their students with technical issues. 

Students will have access to the Tas training material, available for download at edsltas.com and as part of the Tas installation.  If instructor-assisted training for students is desired, it will be offered at a discounted rate.

Trane vs. TAS – Desiccant Wheel Simulation Comparison

Trane vs. TAS – Desiccant Wheel Simulation Comparison

This document shows how TAS Systems can comply with the rated performance of desiccant-based dehumidification systems, as documented by Trane in the Engineering Newsletter volume 34-4. Each different arrangement of desiccant wheel has been modelled in TAS Systems to match the performance of the Trane examples shown via psychometric charts. These have been closely reproduced in TAS.

The performance characteristics have been taken directly from Trane and can be found in the following location:

http://www.trane.com/cps/uploads/userfiles/educationalresources/admapn016en_0905.pdf

1.0 – Wheel Upstream of Cooling Coil

1.1 – Model Comparison

Traditional desiccant dehumidification wheels in a parallel arrangement rotate between two air streams. The regeneration air stream (RG) may be a building exhaust that is used exclusively to reactivate the desiccant. The RG is heated in order to raise the dry bulb temperature and, in turn, lower the relative humidity. This results in water vapour being transferred from the OA stream to the RG’ stream. Although the desiccant wheel removes latent heat (moisture) from the process air stream, sensible heat is added. A cooling coil is often required downstream of the desiccant to cool the air to a practical and usable temperature.

Figure 1 – Trane Wheel upstream of cooling coil model
Figure 2 – TAS Wheel upstream of cooling coil model

1.2 – Psychrometric Chart Comparison

Figure 3 – Trane Psychrometric chart for wheel upstream of cooling
Figure 4 – TAS Psychrometric chart for wheel upstream of cooling

1.3 – Results Table Comparison

 

 Trane temp (F)TAS temp (F)Trane Rel hum (%)TAS rel hum (%)
RG87.087.069.0069.00
RG’250.0250.01.47
RG”135.0134.336.79
OA87.087.069.0069.00
OA’145.0146.84.19
CA77.077.049.0049.13

Figure 5 – Results table for wheel upstream of cooling coil

2.0 – Wheel Downstream of Cooling Coil

Generally speaking, most desiccants adsorb more water vapour as the relative humidity of the process air rises. Desiccants also adsorb more water as the dry bulb temperature of the process air falls. During the cooling season, the coldest part of the system is that which is directly downstream of the cooling coil. It is for this reason that it would be desirable to place the desiccant wheel downstream of the cooling coil, rather than upstream, as in the previous example.
This wheel downstream configuration is mainly used in dedicated outdoor air applications. Relative to the wheel upstream arrangement as used previously, the same dehumidification can be achieved to the same dew point but less or no recooling is required.

2.1 – Model Comparison

Figure 6 – Trane wheel downstream of cooling coil model
Figure 7 – TAS Wheel downstream of cooling coil model

2.2 – Psychrometric Chart Comparison

Figure 8 – Trane Psychrometric chart for wheel downstream of cooling coil
Figure 9 – TAS Psychrometric chart for wheel downstream of cooling coil

2.3 – Results Table Comparison

 

 Trane Temp (F)TAS Temp (F)Trane Rel Hum (%)TAS Rel Hum (%)
RG1061064140.98
RG’114.0114.032.0032.52
RG”106.0106.241.0042.60
CA62.062.096.0096.00
CA’77.076.849.0048.81

Figure 10 – Results table for wheel downstream of cooling

3.0 – Series Desiccant Wheel in a Mixed Air Application

Series regeneration in a desiccant system places the regeneration side of the wheel upstream of the cooling coil and the process side downstream of the coil. Moisture is adsorbed from the process air downstream of the cooling coil and is placed back upstream of the coil. This negates the need for a separate regeneration air stream.

Air leaving the process side of a series desiccant wheel is cooler that the space, making this kind of system good for use in a mixed air stream, with one unit being able to cool and dehumidify the air.

3.1 – Model Comparison

Figure 11 – Trane series desiccant wheel (series regeneration) in a mixed air system model
Figure 12 – TAS series desiccant wheel (series regeneration) in a mixed air system model

3.2 – Psychrometric Chart Comparison

N.B in figure 13, the relevant points for the mixed air flow system are; MA, MA’, CA, SA

Figure 13 – Trane Psychrometric chart for series desiccant wheel in a mixed air application
Figure 14 – TAS Psychrometric chart for series desiccant wheel in a mixed air application

3.3 – Results Table Comparison

 Trane Temp (F)TAS Temp (F)Trane Rel Hum (%)TAS Rel Hum (%)
MA80.080.043.0043.00
MA’74.074.164.0058.02
CA51.051.092.0092.00
SA56.056.962.0063.70

Figure 15 – Results table for wheel in a mixed air application

Closing statement about differing temperature change (5F vs 6F)

Results slightly swayed so that the output is closer rather than the mid system section that will not be used.

4.0 – Series Desiccant Wheel in a Dedicated Outdoor Application

A series desiccant wheel can also be used in a dedicated outdoor application because the wheel adds little sensible heat to the process air. This means that the dry bulb temperature of the process air is cool enough to use. This application can be compared to the ‘Wheel downstream of cooling coil’ arrangement that was considered earlier. In the same conditions the series wheel delivers air at the same dryness but at a cooler temperature than the downstream wheel.

4.1 – Model Comparison

Refer to 3.1 – System layouts used are the same

4.2 – Psychrometric Chart Comparison

Figure 16 – Trane Psychrometric chart for series desiccant wheel in dedicated outdoor application
Figure 17 – TAS Psychrometric chart for series desiccant wheel in dedicated outdoor application

4.3 – Results Table Comparison

 

 Trane Temp (F)TAS Temp (F)Trane Rel Hum (%)TAS Rel Hum (%)
OA87.087.069.0069.00
OA’81.080.987.0085.92
CA58.058.098.0098.99
CA’64.064.177.0076.33

Figure 18 – Results table for a wheel in an outdoor air application

Use of Single Zone VAV Systems

Use of Single Zone VAV Systems

1.0 - Introduction

The purpose of this document is to outline some of the ways TAS Systems has the ability to model single zone VAV systems and their performance characteristics with particular reference to the Trane Engineering newsletter Volume 42-2, entitled ‘Understanding Single-Zone VAV Systems’. The newsletter can be found at the link listed below. Trane Engineering Newsletter Volume 42-2 A single zone constant volume system traditionally uses a temperature sensor in the designated zone in order to vary the cooling and heating capacity, whilst the fan supplies a constant quantity of air. A single zone VAV system, on the other hand, uses the temperature sensor to vary the airflow delivered by the supply fan as well as the heating and cooling capacity in order to maintain the supply air temperature at a set point. Single Zone VAV systems for the most part have been used for large, densely occupied zones that have varying cooling loads. These can include lecture halls, sports halls, and large meeting rooms. As a greater concern for energy consumption develops, single zone VAV is now being increasingly used in smaller zones such as offices, retail stores and classrooms, to take advantage of the energy saving capabilities that can be associated with single zone VAV (SZVAV) systems.

2.0 - Relevant ASHRAE Requirements

Requirements of the ASHRAE Standard 90.1 has certain specifications that single zone VAV systems must comply to. The requirements vary depending on whether cooling coils or direct expansion cooling is utilised. These are listed below;

  1. Air-handling and fan-coil units with chilled-water cooling coils and supply fans with motors greater than or equal to 5 hp shall have their supply fans controlled by two-speed motors or variable-speed drives. At cooling demands less than or equal to 50%, the supply fan controls shall be able to reduce the airflow to no greater than the larger of the following:
    • One-half of the full fan speed, or
    • The volume of outdoor air required to meet the ventilation requirements of Standard 62.1.
  2. Effective January 1, 2012, all air conditioning equipment and air-handling units with direct expansion cooling and a cooling capacity at AHRI conditions greater than or equal to 110,000 Btu/h that serve single zones shall have their supply fans controlled by two-speed motors or variable-speed drives. At cooling demands less than or equal to 50%, the supply fan controls shall be able to reduce the airflow to no greater than the larger of the following:
    • Two-thirds of the full fan speed, or
    • The volume of outdoor air required to meet the ventilation requirements of Standard 62.1.

3.0 - How can TAS Meet These Requirements?

3.1 – First to model the system

The basic model for a single zone VAV system in TAS is shown in figure 1. This uses a heating and cooling coil to vary the temperature of the supplied air with an optimiser used to control the mixing of the outside air and the return air coming back through the system. The heating and cooling coils are controlled by the thermostat in the zone as well as reading the temperature leaving the fan in relation to heating and cooling setpoints.

Figure 2 shows a very similar system that uses direct expansion for the heating and cooling in place of a heating and cooling coil. 

3.1.1 – Optimiser (economiser) in place of dampers

The Trane Engineering newsletter speaks of the implementation of dampers to control airflow. Although TAS has the ability to implement and control the dampers, in this single zone VAV model, TAS has a simpler method of control. An optimiser can be set up so that it will supply as much air as is necessary to the zone from mixing recirculated air and fresh air, whilst ensuring that the minimum fresh air for the zone is met. This is a simpler method for the user to control the ventilation in TAS systems. A complex control circuit would need to be made if dampers were to be used. Figure 6 shows the use of the optimiser in place of the mixing box the Trance Engineering newsletter references. This optimiser is used in both figures 3 and 4. 

3.2 – Minimum flow fan speed – ASHRAE

TAS Systems has the ability to model both cooling and heating coils as well as direct expansion as a means of cooling and heating. The ASHRAE requirements are easily met by inputting some parameters into the software. The requirement A is met in TAS by adjusting the fan properties in a model that uses a cooling coil to generate the cooling capacity. The fan is sized so that it can meet the maximum flow at any one time, whilst the minimum flow source is set to be 0.5x the design flow source. The other requirement, regarding outdoor air ventilation standards is set to ‘all attached zones fresh air’, which is specified in the occupancy conditions of the zone in TAS. In this case there is only one zone attached and the fresh air requirements never exceed one half of the full fan speed. The inputs for this are illustrated in figure 4. Requirement B is similarly implemented in TAS on a model that uses direct expansion to cool and heat the attached zone. The minimum flow on the fan is required to be two thirds that of the full fan speed. This is done by setting the minimum design flow fraction to be 0.6667. Similarly to the previous example, in this case the fresh air requirements will never exceed the two thirds of the full fan speed, meaning that the minimum fan flow rate will be 102.8 l/s during operating hours. The inputs for this are illustrated in figure 5. 

3.3 – CO2-based demand-controlled ventilation

The Trane document outlines how single zone VAV systems are often used for zones that experience largely varying populations. As the population increases, this means the occupants produce more CO2. These zones can be controlled using a carbon dioxide sensor to maintain a comfortable working area with sufficient fresh air to breathe. A carbon dioxide sensor can be used to control an increase in the air flow when the CO2 levels exceed a specified level. This method is implemented into TAS Systems as shown in figure 6. The values for desired CO2 levels can be edited with ease. The blue cross marks the controller monitoring the carbon dioxide, which is located in the exit air stream from the zone being controlled. Another method of controlling this would be to use a damper at the outside air inlet, controlling its opening by a similar CO2 sensor. 

4.0 – Types of Fan control

There are varying methods of controlling single zone VAV systems including how and when they cool or heat and at what flow the supply fan will operate. The three main types of fan control to be looked at are:

  • Constant-speed fan
  • Two-speed fan control
  • Variable-speed fan control

Each method of control is modelled separately in TAS Systems. The constant-speed fan model simply has no controller connected to the fan, meaning that it runs at the sized load whenever the system is in operation. Due to TAS using an hourly sampling system the two-speed fan control cannot be modelled as it would in a real system. This is because it would require instantaneous adjustment and calculation with relation to the flow rate. For this reason, the two-speed fan is modelled the same as the variable speed fan. This can be done because, if the fan speed is say 0.5x the full capacity, this means that a two speed fan will have been doing the same overall work but the speed output TAS gives can be interpreted as a proportion between the two fan speeds that it operates at. The two-speed fan and the variable speed fan are distinguished in their energy consumptions by their differing part load characteristics. Load in a variable speed fan is not directly proportional the power. With a two-speed fan however, it can be assumed that each fan is operating at peak load, allowing it to be modelled by a directly proportional part load characteristic. The variable speed fan differs from this, in that under low loads it uses less power, meaning that it saves on power usage relative to the other two fan control methods. The part-load characteristics are shown below in figure 7. 

5.0 – Energy Savings Associated with SZVAV

As stated and shown in the Trane engineering newsletter, energy savings can be expected by the utilisation of two-speed and variable-speed fans over the dated method of supplying the attached zone with a constant supply of air. Trane supplies results for three different types of fan system, showing how much energy could be saved with the implementation of the two improved fan control methods. Below, figure 8 shows energy consumptions for a classroom in three different locations in America as given by Trane. Figure 9 shows energy savings as found by a simulation in TAS Systems with weather data taken for Sydney, Australia. It can be seen that from the two graphs energy savings are similar for the two-speed and variable-speed fans relative to the constant speed set up. The reasons for the different savings in the Trane and TAS models can be attributed to the varying building size, building layout, climate and operating hours that heavily influence the energy saved. 

6.0 – Improved Part-Load Dehumidification with SZVAV

There is a noticeable difference in the performance of a constant volume system relative to a single zone VAV. The latter improves dehumidification performance at part load conditions. Below in figures 10 and 11, it can be shown graphically via a Trane example and an example done using TAS systems. At part load, the constant speed fan supplies a constant volume of air to the zone. As the sensible cooling load in the zone decreases, the compressor cycles on and off, resulting in warmer air being delivered to the zone. This results in a warmer average coil temperature, meaning that the warmer air has not been dehumidified as much as if it had been cooled more by the single zone VAV system. The single zone VAV system, instead of switching off the compressor, reduces the supply airflow whilst still cooling to the same temperature. This allows more moisture to be removed from the air, giving better dehumidification to the zone. Although more cooling load is applied, more energy is saved from reducing the fan energy. The dehumidification performance values from Trane and TAS Systems are given in Tables 1 and 2 respectively. 

Constant Speed FanVariable Speed Fan
84oF DBT  
Zone Humidity, %RH74%63%
Cooling Loads, tons0.2160.345
Fan Airflow, cfm482291