Air to Water Heat Pumps Monoblock / Split Configurations ...

INTRODUCTION

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Electricity prices have risen significantly in many Canadian provinces and US states. This trend of rising utility rates is expected to continue as federal and local governments push for greater energy efficiency with each new version of the building code. This poses a major challenge for homeowners, designers, contractors, and equipment suppliers, who must develop new products to meet these higher sustainability standards.

With the COVID-19 pandemic, long winters, and an aging population, many Canadians are spending more time at home, leading to an increased demand for natural light in indoor spaces. More natural light requires larger fenestrated building envelopes, which need more energy to maintain acceptable indoor living standards.

Given rising energy prices and tougher environmental regulations, Air to Water (ATW) Heat Pumps offer an affordable solution. These HVAC devices, also known as Mini Air Cooled Chillers in Europe, produce chilled or hot water (or a water/glycol mixture) for space heating, cooling, and domestic hot water (DHW) heating. Equipped with a DC Inverter Compressor and, in split configurations, Enhanced Vapor Injection (EVI) technology, these pumps operate in a temperature range of -25°C to 45°C.

AIR TO WATER (ATW) HEAT PUMPS CONFIGURATIONS

Monoblock Air to Water Heat Pump

A Monoblock ATW Heat Pump is a single unit installed outdoors. In climates with peak winter temperatures below 0°C (32°F), a propylene glycol/water mixture should be used to avoid freezing. The appropriate concentration of glycol depends on the lowest winter temperature. In many major Canadian cities, a 50% water/propylene glycol mixture is used.

Monoblock ATW Heat Pumps require an external pump for circulating the heat transfer fluid (whether water or a water/glycol mixture). During winter, these pumps defrost their evaporators by going into cooling mode, which requires an external heat source. The controller supports modulating speed pumps and includes a PWM (Pulse Width Modulation) control signal for regulating fluid circulation pump speed.

Split Air to Water Heat Pump

A Split ATW Heat Pump consists of two units: an outdoor unit and an indoor unit. The link between these units is made by refrigerant copper lines, eliminating the need for a water/glycol mixture in cold climates. The controller also includes a PWM control signal for the fluid circulation pump. During winter, the pump goes into cooling mode to defrost the evaporator, which requires an external heat source.

ATW Configurations Cost Analysis

Air to Water Heat Pumps can provide either chilled water or hot water and pre-heated DHW, depending on the configuration. The price difference is driven by the cost of the machine, glycol, pump, and manpower.

Heating or Cooling with DHW Pre-Heating

Simultaneous Heating and Cooling with DHW Pre-Heating

The two most common installations of Air to Water Heat Pumps are depicted in the schematics above. The configuration on the left is for places where simultaneous cooling/heating is rare. It uses one tank with an indirect coil to preheat DHW to temperatures as high as 130°F (55°C), and another tank for either space heating or cooling. The configuration on the right uses one indirect tank for DHW pre-heating and space heating, and another tank dedicated to chilled water.

In properties with large fenestrated areas on both the south and north exposures, there may be a cooling demand beside the southern façade and a heating demand beside the northern façade, even in mid-winter temperatures.

• Item
• Monoblock HSS030V2LM
• SPLIT HSS030V2LS
• Heat Pump Selling Price
• 5,235
• 7,521
• 50% Glycol - 16 Pails - Selling Price (required to fill 2 x 40 US Gallons Tanks)
• 3,840
• --
• Manhours Cost for the Installation of Refrigerant Copper Lines Between Indoor and Outdoor Unit
• --
• 480
• Total Cost (CAD $)
• 9,075
• 8,001

CONCLUSION

Even though Monoblock Heat Pumps are cheaper than split ones, the complete installation of a Split ATW heat pump is often less expensive for the customer. Assuming water can be used as a heat transfer fluid in Split Heat Pump installations, the additional cost of high-quality glycol with the proper inhibitor concentration and the cost of a circulation pump make the Monoblock heat pump installation more expensive.

Monoblock Heat Pumps are popular among DIY customers because they appear cheaper before calculating the overall project cost and seem easier to install. In contrast, Split ATW Heat Pumps require professional installation and commissioning of the refrigerant copper lines, which can be less appealing to DIY customers.

Split and monobloc heat pumps: what is the difference in construction?

• Monobloc pumps have the entire refrigeration system in one hermetic unit.

• Split pumps have the refrigeration system split between outdoor and indoor units, with the compressor, evaporator, and expansion valve located outside, and the heat exchanger and circulation pump inside.

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What is the difference between monobloc and split pumps?

Let's examine the most important aspects of the differences in the construction of individual pumps.

Installation of split and monobloc heat pumps

For mono pumps, the entire refrigeration unit is factory-assembled and fully hermetic, ensuring 100% tightness and easier installation without the need for special F-gas licenses. Connections are made only on the water side. In contrast, split devices require part of the refrigeration system to be assembled on-site, connecting both parts of the unit with wires. This increases the risk of losing system tightness, and the installer must have an F-gas license.

Cost

Investing in a split pump usually involves lower initial costs, but additional expenses arise from the need to meet formal requirements, such as creating a product data sheet and regular leak checks by professionals, especially for pumps exceeding 10 kW. Monobloc pumps are more expensive initially but do not generate additional costs later.

Acoustics

Monobloc devices are well-insulated acoustically and thermally, increasing their cost but also providing more comfortable use, as they run quieter. Split pumps tend to be a bit noisier.

Safety and operational reliability

Split pumps risk leakage since part of the refrigeration system is created during installation. However, these devices are better protected against power outages, as the heat exchanger is mounted inside. Monobloc pumps, fully assembled at the factory, reduce the risk of refrigerant leaks but are susceptible to freezing pipes during power outages. Special protections, like insulated water connections using pre-insulated pipes laid below ground frost level, are used to mitigate this risk.

Energy efficiency

Currently, split and monobloc pumps do not differ significantly in performance. Advances in technology have leveled the playing field, so choosing a device from a reputable brand with appropriate power for the building’s energy needs ensures good performance, regardless of the type.

• The operation principle of both types is the same, and they can be equally effective in energy production.
• Split pumps are cheaper but have more demanding installation and additional costs for regular checks and product cards.
• Monobloc pumps are more expensive but run quieter and are less prone to leakage issues. They require additional protection against freezing.

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