Cold beer underfloor heating

Introduction

Underfloor heating from refrigeration waste heat. We recovered cellar cooling and back bar cooler wasted heat and put it back into the pub's underfloor heating.

Venue

Listed building with pre-existing underfloor heating. Independently located remote heat circuits including refrigeration heat recovery and boiler.

Wiring

We use a 13 amp switched outlet to supply power to the first control application in the system, this is the digital weather monitoring system. The weather monitor switch circuit works by monitoring the external air temperature, relaying back information through a probe to the digital controller. As the weather changes the digital controller manages the renewable and conventional heat provision.

Within this control circuit are two cylinder thermostats. The cylinder thermostats control the RRH circulation pump and the 3-way heat recovery valve located on the refrigeration condensing unit. The digital weather controller also powers the boiler via the upper level primary coil thermostat.

To sum up the control system the weather system directs the overall operation of the heat.

The wiring circuit, water circuit and refrigeration system diagram can be view further in this article.

Refrigeration 3-Way Recovery Valve

The 3-way valve is installed between the compressor high side, air condenser, water condenser and the condensing unit liquid receiver.

When the valve is energised, hot gas is redirected to the recovery condenser (water). When the valve is de-energised the hot gas flows through the condensing unit fan cooled condenser.

This creates a dual condensing unit that can do air or water switching automatically between the two according to the high pressure refrigerant temperature.

The parts we used for this and the installation process is beyond the scope of this article. For more details, Google “Sporlan threeway recovery valve”

Refrigeration Recovery Heat (RRH) Control

Looking at the RRH control system in more detail, the power supply to the RRH water circulation pump and heat recovery 3-way valve passes through a delay-on-timer and a single pole contactor. The contactor energises using the compressor contactor refrigeration control circuit. If the condensing unit is not running because all coolers have reached temperature, the power supplier is isolated to the RRH water pump and the 3-way heat recovery valve. We configured the control of these parts so the pump and the 3-way valve are deactivated when the all coolers are at temperature as there will be no heat generated.

The delay-on-timer was installed to prevent short cycle starts, therefore power is only switched when the system is running on a full cooling cycle more than 45 seconds.

RRH Refrigeration High Pressure Control

Safeguarding against high pressure overload the refrigeration system high pressure stays within the system operating pressure range, a controller and sensor is installed between the renewable contactor power supply and the 3-way valve. When hot gas flowing through the water heat exchanger has reached its higher range limit, the 3-way valve power is stopped by the controller and the hot gas is redirected to the fan cooled air condenser. A differential temperature was set so that the controller activates the 3-way valve only when the hot gas pressure has lowered to the middle pressure range value.

Additionally, there are also a range of other methods we could have used to achieve a balanced refrigeration high pressure dual condensing system. One of which would be to use a hot gas bypass valve set to open and close within a pressure range, which would redirect some of the gas from the water condenser to the air condenser. This would in turn allow both the water condenser and the air condenser to deliver liquid to the receiver. The limitations with a hot gas high pressure value are that refrigerate will reside in both of the condenser refrigeration piping circuits simultaneously.

RRH Exchanger

This is a brazed plate exchanger for refrigerant hot gas to water heat exchange. The size of this type of heat exchanger varies depending on the condensing kW output of the refrigeration system. The one we use fitted compact within the condensing unit housing, underneath the condenser fan. This heat exchanger works exactly the same as a water cooled refrigeration condensing unit. Heat produced from the the compressor hot gas vapor heats the water and also acts as a condenser to cool and convert the R134a refrigerant into supercooled liquid. We measured the temperature of the hot refrigerant discharge pipe of the compressor and recorded a high of 61c when the condensing unit was operating within an outside temperature of -2c. This hot gas temperature is not a constant and will fluctuate based on the temperature of vapor returning from the system's evaporators and the number of evaporators calling for cooling, we achieved 45c to 60c respectively while monitoring this aspect of the system for several days.

The distance of the RRH exchange to the cylinder has a direct effect on the temperature of the water being circulated within the water circuit. The longer the pipes from the cylinder to the heat exchange the greater the time it will take to heat all the water in the circuit to 45c and the enclosed static water of the cylinder.

We used a 2" thick wall insulation on water pipes going to and from the cylinder and heat exchanger so as to insulate against heat lost through pipes. Therefore the length of this water circuit should be kept as short as possible to reduce the loss of water heat flowing through this part of the system. The RRH exchanger was installed with a thermal wrap around the full body of the exchanger to reduce heat lost at this part of the system.

In are particular system the water RRH water pipe circuit was submersed 1m underground and encapsulated in a 200mm diameter, 10mm wall drainage pipe for total pipe and cable protection against excavation, subsidence and frost. The location of the installation was in the north of the UK with the lowest recorded temperatures of -10c during parts of winter.

RRH System (Refrigeration, Heating, Wiring and Control)

Weather Sensor

The weather sensor can be adjusted to optimise the indoor temperature based on what is happening outside. When it is too warm outside to have the heating on inside then the weather sensor controls the amount of heat produced. If there is a cold snap during certain times of the year then this setting will enable the cylinder to be provided with heat from the boiler and the refrigeration system heat exchanger.

Care most be taken when placing the outdoor weather sensor. Things like direct sunlight and other sources of heat like boiler flues and other machinery that are giving off heat nearby. The weather sensor must be adjusted slightly over a period of 1-2 weeks in the colder periods of the year to get the best indoor temperature based on what is happening outside of the building. The best time to adjust the weather sensor is when the weather is warming up outside and is warm enough to not need heating inside. (See figure 1)

The weather sensor was custom made, as at the time of system installation we could not find an independent option that was not associated with specific boilers.

In general the temperature outside would be below 17c to 18c before the weather sensor allows the boiler and renewable heat system to warm up the cylinder this warm up temperature is dependent on a range of factors within the property, and can alter this figure based on wall insulation, other heat sources within the build, windows and doors and the facing position of the heated area of the property . The differential is 3 degrees, allowing a 3 degree rise before switching off the heating systems.

Triple Coil Indirect Unvented Hot Water Cylinder.

The unvented cylinder we used has 3 closed circuit coils, each submersed within the bulk of water held by the cylinder. In our system we connected the boiler to the primary coil. The secondary top coil, also know as the Tertiary coil was used to connect the underfloor heating matrix. The lower renewable coil is where we connected the RRH exchanger. The primary coil and the renewable coil both contribute heat and the Tertiary coil transfers this heat to the underfloor heating matrix conducted via the cylinder water. The cylinder we used also has an electric immersion heater. In this case we did not connect this immersion heat although this could potentially be connect to an electrical power source in order to provide an additional backup should the boiler and the renewable coil heat sources both fault to provide sufficient heat.

In the case of our system, the 3 coil cylinder is being used in a different way to a conventional unvented cylinders. In most cases the cylinder is connected direct to the water mains through the cold water inlet and the outlet is then connected to the running hot water system to supply taps. We have capped of the outlet with an auto pressure air vent and terminated after this with a cock-tap, and this is used as an air bleed tap for when we first filled the cylinder. The water in the cylinder remains static and it's definitive purpose is to transfer heat from the boiler and renewable coil to the under floor heating coil. In effect the cylinder is a heat exchanger.

We used the 3 coil cylinder to enable the three separate systems to work independently and to control the temperature of the water flowing through the underfloor heating. A constant 45c through the underfloor heating is achieved. Some refrigerant water heat exchange systems push heat to a water system regardless of the temperature required. In our system we can maintain a temperature that is no greater than 45c. This means we have full independent control over all systems even if the hot gas temperature rises to 60c the renewable coil on the cylinder will always provide a heat source that is 45c or less.

Underfloor Heating System

Approx floor area 10m x 10m

Total loop length @ 200mm centers: 400m

Total litres in loop: 56 litres

Water start temperature: 18c

Water satisfied temperature: 45c

Water flowrate: 12 litre/Min

Kw required for 1hr warmup: 25Kw approx

Kw required for maintained room temperature @ 22c: 4.2kw

RRH Contribution

1Hr Warmup: 10% - 15%

Maintained: 40 – 58%

RRH Exchanger

Refrigeration heat exchanger output water temperature: 45c to 60c

Hot gas temperature: 61c @ -2c ambient

Max kW: 5.9

Min kW: 2

Refrigeration on per hour: 15 - 25mins

Remote cellar room

The cellar was constructed from 80mm insulated panels and lined with 3mm 5-bar plating to ensure barrel don't damage the insulated walls. The base of the room uses hard gain sand to allow drainage away from the floor. Externally the room was clad with treated redwood and a powder coated steel roof to protect against the elements.

Refrigeration system commissioned by a F-Gas registered engineer

Cylinder and water system commissioned by a G3 engineer.

Venue