Radiant Control system – temperature control guide

Introduction

The house is a massive design, very slow to change temperature and the system aims to keep the house at a steady temperature all year long while allowing natural use.  This means in the cold months it keeps very precise control of heating effort using industrial algorithms to target temperature within 0.1 degree , in the cooling period it is designed to be “natural”, allowing for some drift, as if in a cave or sheltered grove, rather than strict like conventionally air conditioned space.  In the shoulder seasons, opening windows etc. when desired is anticipated.  In the dead of winter and during heat waves they should be shut.

The system does not provide dehumidification, a dehumidifier should be run during the summer months to keep the humidity in the house lower than 55-60%.

This house has significant passive solar gains in winter and was designed to be a little warm on sunny days in the winter.

The temperature control has been developed to control hydronic systems using low temperature heating and high temperature cooling strategies.  Its goal is room temperature control within 0.1 degree of setpoint in cold weather.  It is designed to compensate for high latency or high mass assemblies often found in hydronic systems and the passive effects such as solar or internal gains.

The system encompasses a physical thermostat and a system of network based sensors, accessible on the local network. It includes sensors for room temperature, humidity, outdoor air temperature, and operating temperature.

Most of the functionality for the control system is accessed over the network, through a web browser or dedicated Android App.

Temperature Control

The basic Thermostat control allows setting the setpoint turning on and off night setback, and turning the system to standby.

The thermostat setting applies to heating as well as cooling.

36 Hour Chart

The 36 hour chart gives the heating/cooling performance versus setpoint,  indoor , outdoor temperature, some analysis is possible from this screen.

By calculating from the slope of changes to the inside temperature, setpoint and HP effort can be used to adjust or tune the PID parameters.

By comparing the upper chart to the lower, specifically changes to the inside temperature vs the outdoor temperature and HP effort, one can deduce passive effect.

Setup

The settings screen allows the basic operating variables to be setup, most of these settings need only be “tuned” once or very occasionally, and with the exception of the setback times and value, should be done by a person who understands the meaning of each parameter.

Reset Balance – outside temp.

This refers to the outside temperature below which heating is needed in Celsius.  This value is used to start heat and used in calculating the proportional effort portion of the PID using the reset ratio and Proportional boost explained below.  The value depends on likely passive heat generation. Poorly insulated houses could have a balance as high as the setpoint, very well insulated homes will be lower, depending on the level of passive gains that can be relied on.   If estimating, it is better to set it a little high rather than too low.

The balance temperature for cooling is the same as the setpoint.

Reset Ratio

This refers to the design temperature of the fluid used in heating as compared to the outside temperature and setpoint.  For example for heating, if the balance point is 15, the outside temperature is 5, the setpoint is 20 and the desired fluid temperature is 30, the ratio should be 1.0 if the desired fluid temperature is 25 the ratio should be 0.5.

It can be calculated using heat loss and dividing by the surface area exposed for heating in the system and adjusting for the estimated emissivity of the radiating surfaces .  A high performance house with a low heat loss and a large radiating area will have a low ratio.

Proportional boost

The proportional boost is needed to compensate for heating system hysterisis and give some “headroom” for the system , the minimum is 2, if in doubt set it for 5.

PID Integral, seconds

The Integral is the primary way the system can compensate for the tendency of proportional systems to stop short or overshoot the setpoint.  Set this for the time it takes to heat the home 1 degree at maximum power.  A radiant system in embedded concrete slabs may be 12 hours, in seconds, a hydronic system with radiators may be 1.5 hours etc.

PID Derivitive, seconds

The derivative “softens” the PI algorithm, a shock absorber to reduce swings , should be set for less than 25% of the integral, during the tuning, try it at 0 to see if it is even a problem, then gradually ramp up the value.

Nightime setback start time

Set the time for daily setback to begin, hours in a 24 clock.

Nightime setback finish time

Set the time for daily setback to begin, hours in a 24 clock.

Setback degrees

The amount of the setback in degrees.

Use Solar Heat Minimum temperature

If your system is equiped with a solar heat transfer system, set the tank minimum temperature to use solar heat as a default over generated heat.

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