Run Simulations Online

If you run simulations fast and easy, the JESS Online service is for you.

JESS Online quick link

Power and Speed

Our Simulation Stations offer power and speed to suit your needs.

Simulation stations quick link

Research & Development

We can help you develop your own solutions with our technologies.

We Are the Experts

On building energy modelling, optimization, and computing.


If you want to access JESS from DesignBuilder or the standalone JESS client, you can start with the built-in trial account which contains 5 computing hours free to use. Follow the animation on the bottom of this page to enable it. The trial account does not let you access the new online features such as job management and viewers, though.

To create a standard JESS account, please follow the steps here:

1. Go to and create an account there

You will just need to provide a name and a valid email address to create an account on the web portal. A verification email containing a link to set password will be sent to your mailbox. Please check the spam filter if the email is not received.

2. Log on and go to My Account

You can request a JESS account on the second tab ("JESS Account"). You will be asked to fill in some contact details before your JESS account is created. You should receive an email containing the credentials and information about the JESS service if successful. 

3. In DesignBuilder or the JESS client, log on with the received JESS username and password

You will have 10 hours in the account to start using JESS straightaway. To top-up, use the third ("My Invoices") tab on the My Account page.

Please feel free to contact This email address is being protected from spambots. You need JavaScript enabled to view it. if you have any questions.  



JESS stands for Java EnergyPlus Simulation Server. It is a software system we have developed to provide remote simulation solutions to EnergyPlus users. JESS Online is the online service with which you can run time-consuming simulation jobs on our high-performance computers. Not only it will free up your computer for other tasks while you are waiting for the results, but running simulations on JESS will also return you results quicker in most cases. Especially, with JESS's acceleration method, simulations can be 5-10 times faster than a standard run. This will let you do a lot more analysis using the model and hence producing better designs.

 JESS service


Why use online simulation?

Online simulation is an emerging technology for architectural design and engineering fields. It gives you the ability to access fast computing resources to run multiple simulations in parallel, and lets you do more creative works while waiting for the results. It enables a whole new workflow of handling models and let you do things that were "impossible" before.

Read more

What is the advantage of JESS?

JESS started its life in 2011 and has grown into probably the most reliable and mature online EnergyPlus simulation service available. To date, it has been tested by over 600 users and executed nearly one million hours of simulations. Performance and compatibility are the key advantages of JESS. We use only the standard releases of EnergyPlus (all versions from 7.0 and above) to ensure the best compatibility. Even with the acceleration method, the results produced by JESS are faithful and compatible with the standard outputs in the majority of cases. 

Read more

How much does it cost?

The JESS service is charged at a flat rate of £0.25 (ex. tax) per hour of computing time. You will be invoiced on a "pay-as-you-go" basis, which means you only pay for what you have used. If you just want to test the system and see how it works, you can get a trial account with 5 hours of simulation time free of charge.


How to get started?

JESS is supported by a number of building simulation tools. For example, DesignBuilder has built-in JESS support for both standard/accelerated simulation and optimisation runs. You may also download the standalone JESS Client program, which lets you connect to JESS from all sorts of tools including OpenStudio, EP-Launch, Matlab, and so on. To get started, please first fill in the form for requesting a JESS account.

Read more


Use JESS with DesignBuilder
Run simulation on JESS from DesignBuilder


Getting started with JESS is straightforward. All you need is a JESS client or a building simulation tool already supporting JESS.

DesignBuilder - JESS link

DesignBuilder Software

The latest version of DesignBuilder software has the JESS support built-in. The animation above shows how you can set up a simulation to be run on JESS with only a few clicks. To test the service, you can use the trial account and do not need to send any personal information to us. The trial account gives you 5 hours of computing time, which is enough for thousands of runs of a simple model, or a few large models.

Using the JESS Client

Download button

If you are using EnergyPlus with other tools or in your own development, the JESS Client can normally replace the local simulation command and give you the remote simulation capability. You can find more details of the JESS Client on its manual pages. Detailed examples are provided for using it with GenOpt, EP-Launch, Matlab and other tools. You can download the JESS Client package here.

How to get an account

New users of JESS can request a free trial account directly from the JESS Client GUI. No registration or personal details are required. This temporary account gives you 5 hours of computing time, and you can start testing the service straight away. 


To get more time for testing, or to start using it for your work, you need to get in touch with your contact details, either by dropping us an email at This email address is being protected from spambots. You need JavaScript enabled to view it. or by filling out the form for Requesting a JESS Account. We will create your own JESS account and send you the details, including pricing and payment options.


Click on the screenshot below to access the JESS web portal for users. You need your own JESS account to access the user's portal. 


Web portal screenshot

JESS Online of ENSIMS is a reliable and easy-to-use service that offers you a cost-effective solution to your simulation computing needs. Here is a summary of the main features.

Simulation speed

During our research and development, we have made every effort to optimize the hardware and software platform in order to achieve the best simulation speed. As you can see in the performance tests, our system consistently outperforms the best instance available on the public clouds (Amazon AWS EC2 as tested). This means you can get the results back quicker from JESS Online than anywhere else.

Easy to use

Using JESS does not require any special knowledge about networking, remote simulation or cloud computing. With the building simulation tools have already JESS support implemented, the process is as simple as getting an account (or using a free trial account) and log on. All your existing workflows may remain the same. Unlike most of the cloud services, you do not need to worry about setting up keys, starting and terminating computing nodes, or managing separate accounts. Usage of JESS Online is charged by the actual computing time of the simulation jobs. You can check your usage and the progress of the on-going jobs with the online user's portal.  

Compatibility and support

JESS Online does not tie you to one building simulation tool. In fact, we are working to support as many building simulation tools as we can. At the present, this service supports only EnergyPlus, Radiance and Daysim simulations. More simulation engines will be added in the future. Our support team is friendly and eager to help you with your problems and requests.

New opportunities

Another significant advantage of JESS is its native support for jEPlus projects. This provides an ideal solution for consultancy and research works where large-scale parametric analysis, uncertainty/sensitivity analysis and optimisation are used. We are here to support your development and help you create customized solutions for your particular tasks. 

Supported Software

Our solutions are designed for:

More to come, soon!

Go to top